Remove the underflow checks because the method already requires that Position points to a valid location.
Remove the underflow checks because the method already requires that Position points to a valid location.

Swift SVN r25813

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