REPL: Don't crash if there is no module loader.
REPL: Don't crash if there is no module loader.

Fixes <rdar://problem/13309288>.

Swift SVN r4232

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