[Driver] Don't reuse a possibly-invalidated iterator.
[Driver] Don't reuse a possibly-invalidated iterator.

No test case; this is apparently hitting Enrico but not reproducing in
any obvious way for me. Nevertheless, it /could/ be an issue, so let's be
conservative.

rdar://problem/20402875

Swift SVN r26882

cbrentharris/swift,dduan/swift,therealbnut/swift,JaSpa/swift,zisko/swift,johnno1962d/swift,shahmishal/swift,kusl/swift,tjw/swift,kentya6/swift,hughbe/swift,jopamer/swift,shajrawi/swift,atrick/swift,practicalswift/swift,gregomni/swift,modocache/swift,hooman/swift,shajrawi/swift,parkera/swift,swiftix/swift.old,jmgc/swift,kstaring/swift,kentya6/swift,LeoShimonaka/swift,practicalswift/swift,zisko/swift,jtbandes/swift,uasys/swift,felix91gr/swift,mightydeveloper/swift,austinzheng/swift,modocache/swift,milseman/swift,roambotics/swift,alblue/swift,xedin/swift,cbrentharris/swift,kusl/swift,natecook1000/swift,gribozavr/swift,kperryua/swift,emilstahl/swift,danielmartin/swift,LeoShimonaka/swift,arvedviehweger/swift,swiftix/swift.old,nathawes/swift,jckarter/swift,OscarSwanros/swift,uasys/swift,tinysun212/swift-windows,shajrawi/swift,cbrentharris/swift,karwa/swift,calebd/swift,tjw/swift,return/swift,glessard/swift,ben-ng/swift,zisko/swift,OscarSwanros/swift,gribozavr/swift,codestergit/swift,sdulal/swift,Jnosh/swift,kperryua/swift,apple/swift,brentdax/swift,lorentey/swift,xedin/swift,Jnosh/swift,jmgc/swift,karwa/swift,swiftix/swift,hughbe/swift,gottesmm/swift,jopamer/swift,xwu/swift,swiftix/swift,khizkhiz/swift,frootloops/swift,cbrentharris/swift,cbrentharris/swift,gregomni/swift,CodaFi/swift,cbrentharris/swift,KrishMunot/swift,arvedviehweger/swift,hooman/swift,tkremenek/swift,parkera/swift,benlangmuir/swift,IngmarStein/swift,shajrawi/swift,IngmarStein/swift,JaSpa/swift,modocache/swift,austinzheng/swift,rudkx/swift,johnno1962d/swift,mightydeveloper/swift,jopamer/swift,manavgabhawala/swift,djwbrown/swift,xedin/swift,KrishMunot/swift,jtbandes/swift,atrick/swift,natecook1000/swift,djwbrown/swift,aschwaighofer/swift,tinysun212/swift-windows,parkera/swift,russbishop/swift,devincoughlin/swift,natecook1000/swift,KrishMunot/swift,arvedviehweger/swift,roambotics/swift,tardieu/swift,CodaFi/swift,austinzheng/swift,tinysun212/swift-windows,CodaFi/swift,sschiau/swift,stephentyrone/swift,gregomni/swift,karwa/swift,johnno1962d/swift,arvedviehweger/swift,felix91gr/swift,danielmartin/swift,gmilos/swift,frootloops/swift,kusl/swift,frootloops/swift,IngmarStein/swift,OscarSwanros/swift,tinysun212/swift-windows,gregomni/swift,apple/swift,calebd/swift,bitjammer/swift,return/swift,slavapestov/swift,milseman/swift,practicalswift/swift,devincoughlin/swift,kentya6/swift,IngmarStein/swift,kperryua/swift,SwiftAndroid/swift,natecook1000/swift,atrick/swift,ken0nek/swift,xedin/swift,milseman/swift,khizkhiz/swift,sschiau/swift,JGiola/swift,allevato/swift,devincoughlin/swift,Ivacker/swift,practicalswift/swift,gribozavr/swift,SwiftAndroid/swift,amraboelela/swift,harlanhaskins/swift,codestergit/swift,kstaring/swift,harlanhaskins/swift,kentya6/swift,codestergit/swift,LeoShimonaka/swift,swiftix/swift.old,adrfer/swift,milseman/swift,slavapestov/swift,gregomni/swift,mightydeveloper/swift,sdulal/swift,xwu/swift,ahoppen/swift,xedin/swift,khizkhiz/swift,dduan/swift,jtbandes/swift,kusl/swift,khizkhiz/swift,gribozavr/swift,amraboelela/swift,nathawes/swift,nathawes/swift,shahmishal/swift,kperryua/swift,danielmartin/swift,sdulal/swift,felix91gr/swift,gribozavr/swift,emilstahl/swift,modocache/swift,brentdax/swift,johnno1962d/swift,parkera/swift,OscarSwanros/swift,gregomni/swift,shahmishal/swift,arvedviehweger/swift,frootloops/swift,slavapestov/swift,tkremenek/swift,deyton/swift,swiftix/swift,return/swift,Jnosh/swift,JGiola/swift,brentdax/swift,aschwaighofer/swift,huonw/swift,karwa/swift,xwu/swift,shahmishal/swift,sdulal/swift,milseman/swift,CodaFi/swift,airspeedswift/swift,calebd/swift,tjw/swift,JaSpa/swift,frootloops/swift,mightydeveloper/swift,lorentey/swift,ben-ng/swift,tjw/swift,Ivacker/swift,djwbrown/swift,karwa/swift,OscarSwanros/swift,jckarter/swift,gribozavr/swift,huonw/swift,huonw/swift,JGiola/swift,danielmartin/swift,manavgabhawala/swift,slavapestov/swift,kentya6/swift,adrfer/swift,lorentey/swift,parkera/swift,emilstahl/swift,JaSpa/swift,alblue/swift,aschwaighofer/swift,LeoShimonaka/swift,swiftix/swift.old,jmgc/swift,swiftix/swift,manavgabhawala/swift,dduan/swift,ken0nek/swift,danielmartin/swift,nathawes/swift,MukeshKumarS/Swift,tardieu/swift,felix91gr/swift,harlanhaskins/swift,russbishop/swift,JGiola/swift,adrfer/swift,jmgc/swift,natecook1000/swift,gmilos/swift,lorentey/swift,jckarter/swift,devincoughlin/swift,shajrawi/swift,milseman/swift,stephentyrone/swift,rudkx/swift,nathawes/swift,jtbandes/swift,arvedviehweger/swift,djwbrown/swift,djwbrown/swift,CodaFi/swift,zisko/swift,codestergit/swift,ken0nek/swift,kstaring/swift,dduan/swift,brentdax/swift,MukeshKumarS/Swift,alblue/swift,stephentyrone/swift,uasys/swift,khizkhiz/swift,benlangmuir/swift,sschiau/swift,hughbe/swift,alblue/swift,IngmarStein/swift,cbrentharris/swift,SwiftAndroid/swift,jtbandes/swift,shahmishal/swift,xedin/swift,allevato/swift,hooman/swift,airspeedswift/swift,kentya6/swift,KrishMunot/swift,zisko/swift,kstaring/swift,mightydeveloper/swift,atrick/swift,JGiola/swift,hooman/swift,manavgabhawala/swift,apple/swift,ben-ng/swift,hughbe/swift,hooman/swift,alblue/swift,ben-ng/swift,tardieu/swift,allevato/swift,ben-ng/swift,parkera/swift,deyton/swift,practicalswift/swift,sdulal/swift,xwu/swift,stephentyrone/swift,practicalswift/swift,Ivacker/swift,khizkhiz/swift,adrfer/swift,benlangmuir/swift,devincoughlin/swift,zisko/swift,jtbandes/swift,sschiau/swift,Ivacker/swift,parkera/swift,codestergit/swift,hooman/swift,bitjammer/swift,MukeshKumarS/Swift,jmgc/swift,swiftix/swift.old,gmilos/swift,russbishop/swift,calebd/swift,uasys/swift,return/swift,bitjammer/swift,kusl/swift,bitjammer/swift,jckarter/swift,bitjammer/swift,adrfer/swift,jopamer/swift,shahmishal/swift,ahoppen/swift,therealbnut/swift,karwa/swift,swiftix/swift,jmgc/swift,devincoughlin/swift,harlanhaskins/swift,arvedviehweger/swift,xwu/swift,Jnosh/swift,jckarter/swift,IngmarStein/swift,jckarter/swift,felix91gr/swift,tinysun212/swift-windows,deyton/swift,ken0nek/swift,xedin/swift,harlanhaskins/swift,ahoppen/swift,djwbrown/swift,stephentyrone/swift,jmgc/swift,adrfer/swift,felix91gr/swift,slavapestov/swift,apple/swift,ahoppen/swift,russbishop/swift,hooman/swift,emilstahl/swift,Ivacker/swift,roambotics/swift,karwa/swift,kstaring/swift,ahoppen/swift,atrick/swift,natecook1000/swift,jtbandes/swift,shajrawi/swift,glessard/swift,hughbe/swift,uasys/swift,milseman/swift,sschiau/swift,harlanhaskins/swift,JaSpa/swift,tkremenek/swift,kperryua/swift,kusl/swift,Ivacker/swift,gribozavr/swift,ken0nek/swift,ken0nek/swift,alblue/swift,allevato/swift,lorentey/swift,rudkx/swift,practicalswift/swift,codestergit/swift,ben-ng/swift,IngmarStein/swift,allevato/swift,amraboelela/swift,gottesmm/swift,tardieu/swift,parkera/swift,roambotics/swift,JGiola/swift,aschwaighofer/swift,swiftix/swift.old,sdulal/swift,tjw/swift,sdulal/swift,swiftix/swift,huonw/swift,uasys/swift,kentya6/swift,glessard/swift,airspeedswift/swift,JaSpa/swift,brentdax/swift,KrishMunot/swift,return/swift,tkremenek/swift,glessard/swift,ben-ng/swift,stephentyrone/swift,johnno1962d/swift,mightydeveloper/swift,rudkx/swift,Jnosh/swift,benlangmuir/swift,SwiftAndroid/swift,swiftix/swift.old,shajrawi/swift,therealbnut/swift,deyton/swift,calebd/swift,tardieu/swift,apple/swift,amraboelela/swift,dduan/swift,gmilos/swift,xwu/swift,gottesmm/swift,bitjammer/swift,LeoShimonaka/swift,shahmishal/swift,allevato/swift,natecook1000/swift,swiftix/swift,emilstahl/swift,harlanhaskins/swift,aschwaighofer/swift,tardieu/swift,lorentey/swift,tkremenek/swift,CodaFi/swift,apple/swift,therealbnut/swift,kstaring/swift,modocache/swift,austinzheng/swift,MukeshKumarS/Swift,ahoppen/swift,OscarSwanros/swift,modocache/swift,xedin/swift,austinzheng/swift,ken0nek/swift,kusl/swift,return/swift,alblue/swift,slavapestov/swift,LeoShimonaka/swift,gottesmm/swift,therealbnut/swift,return/swift,aschwaighofer/swift,sschiau/swift,CodaFi/swift,dreamsxin/swift,huonw/swift,gottesmm/swift,SwiftAndroid/swift,airspeedswift/swift,tjw/swift,huonw/swift,OscarSwanros/swift,calebd/swift,dreamsxin/swift,aschwaighofer/swift,sdulal/swift,KrishMunot/swift,glessard/swift,devincoughlin/swift,austinzheng/swift,allevato/swift,tinysun212/swift-windows,brentdax/swift,devincoughlin/swift,codestergit/swift,practicalswift/swift,therealbnut/swift,Jnosh/swift,Jnosh/swift,gmilos/swift,gribozavr/swift,emilstahl/swift,shajrawi/swift,calebd/swift,frootloops/swift,glessard/swift,Ivacker/swift,kperryua/swift,johnno1962d/swift,karwa/swift,felix91gr/swift,sschiau/swift,gmilos/swift,danielmartin/swift,johnno1962d/swift,LeoShimonaka/swift,swiftix/swift.old,nathawes/swift,tkremenek/swift,uasys/swift,cbrentharris/swift,brentdax/swift,nathawes/swift,dduan/swift,benlangmuir/swift,xwu/swift,gottesmm/swift,lorentey/swift,lorentey/swift,airspeedswift/swift,russbishop/swift,rudkx/swift,deyton/swift,roambotics/swift,frootloops/swift,amraboelela/swift,danielmartin/swift,manavgabhawala/swift,hughbe/swift,gmilos/swift,gottesmm/swift,khizkhiz/swift,SwiftAndroid/swift,modocache/swift,deyton/swift,atrick/swift,rudkx/swift,emilstahl/swift,hughbe/swift,deyton/swift,jopamer/swift,emilstahl/swift,kperryua/swift,manavgabhawala/swift,MukeshKumarS/Swift,shahmishal/swift,airspeedswift/swift,tardieu/swift,amraboelela/swift,huonw/swift,kusl/swift,therealbnut/swift,benlangmuir/swift,stephentyrone/swift,airspeedswift/swift,adrfer/swift,tinysun212/swift-windows,jopamer/swift,russbishop/swift,tjw/swift,SwiftAndroid/swift,JaSpa/swift,kstaring/swift,Ivacker/swift,djwbrown/swift,zisko/swift,LeoShimonaka/swift,amraboelela/swift,jopamer/swift,jckarter/swift,KrishMunot/swift,sschiau/swift,roambotics/swift,MukeshKumarS/Swift,tkremenek/swift,mightydeveloper/swift,bitjammer/swift,MukeshKumarS/Swift,kentya6/swift,austinzheng/swift,slavapestov/swift,dduan/swift,manavgabhawala/swift,mightydeveloper/swift,russbishop/swift