Fix potential crash on Windows: off-by-one in malloc()
Fix potential crash on Windows: off-by-one in malloc()

Spotted by gdb's malloc debugger while I was looking for something else.

ryantm/ghc,wxwxwwxxx/ghc,forked-upstream-packages-for-ghcjs/ghc,urbanslug/ghc,TomMD/ghc,ezyang/ghc,hferreiro/replay,snoyberg/ghc,nushio3/ghc,vTurbine/ghc,lukexi/ghc-7.8-arm64,mcschroeder/ghc,lukexi/ghc-7.8-arm64,snoyberg/ghc,mettekou/ghc,siddhanathan/ghc,GaloisInc/halvm-ghc,lukexi/ghc,spacekitteh/smcghc,sgillespie/ghc,mfine/ghc,nathyong/microghc-ghc,ezyang/ghc,vikraman/ghc,jstolarek/ghc,siddhanathan/ghc,mfine/ghc,fmthoma/ghc,gridaphobe/ghc,GaloisInc/halvm-ghc,fmthoma/ghc,wxwxwwxxx/ghc,nushio3/ghc,ryantm/ghc,tibbe/ghc,tibbe/ghc,green-haskell/ghc,nushio3/ghc,ml9951/ghc,oldmanmike/ghc,forked-upstream-packages-for-ghcjs/ghc,ml9951/ghc,lukexi/ghc,hferreiro/replay,vTurbine/ghc,mfine/ghc,mettekou/ghc,elieux/ghc,gcampax/ghc,ml9951/ghc,green-haskell/ghc,tjakway/ghcjvm,nkaretnikov/ghc,ml9951/ghc,spacekitteh/smcghc,green-haskell/ghc,forked-upstream-packages-for-ghcjs/ghc,forked-upstream-packages-for-ghcjs/ghc,mfine/ghc,mcschroeder/ghc,oldmanmike/ghc,ekmett/ghc,sdiehl/ghc,anton-dessiatov/ghc,ilyasergey/GHC-XAppFix,sgillespie/ghc,olsner/ghc,snoyberg/ghc,acowley/ghc,lukexi/ghc-7.8-arm64,spacekitteh/smcghc,TomMD/ghc,fmthoma/ghc,vikraman/ghc,mcmaniac/ghc,nushio3/ghc,christiaanb/ghc,vTurbine/ghc,da-x/ghc,nomeata/ghc,spacekitteh/smcghc,vTurbine/ghc,hferreiro/replay,da-x/ghc,ezyang/ghc,elieux/ghc,nkaretnikov/ghc,acowley/ghc,AlexanderPankiv/ghc,gridaphobe/ghc,christiaanb/ghc,jstolarek/ghc,olsner/ghc,mettekou/ghc,nathyong/microghc-ghc,elieux/ghc,gridaphobe/ghc,tjakway/ghcjvm,GaloisInc/halvm-ghc,forked-upstream-packages-for-ghcjs/ghc,da-x/ghc,nkaretnikov/ghc,shlevy/ghc,vikraman/ghc,sgillespie/ghc,lukexi/ghc,ml9951/ghc,lukexi/ghc-7.8-arm64,wxwxwwxxx/ghc,fmthoma/ghc,vikraman/ghc,ryantm/ghc,sdiehl/ghc,nathyong/microghc-ghc,ilyasergey/GHC-XAppFix,oldmanmike/ghc,tibbe/ghc,bitemyapp/ghc,christiaanb/ghc,spacekitteh/smcghc,gridaphobe/ghc,elieux/ghc,nomeata/ghc,ghc-android/ghc,mcmaniac/ghc,nkaretnikov/ghc,sdiehl/ghc,sdiehl/ghc,ezyang/ghc,shlevy/ghc,anton-dessiatov/ghc,tjakway/ghcjvm,GaloisInc/halvm-ghc,mettekou/ghc,oldmanmike/ghc,ekmett/ghc,gridaphobe/ghc,ml9951/ghc,mcschroeder/ghc,shlevy/ghc,elieux/ghc,gcampax/ghc,olsner/ghc,snoyberg/ghc,fmthoma/ghc,nomeata/ghc,tibbe/ghc,acowley/ghc,oldmanmike/ghc,TomMD/ghc,nushio3/ghc,gcampax/ghc,ekmett/ghc,hferreiro/replay,tjakway/ghcjvm,lukexi/ghc-7.8-arm64,nathyong/microghc-ghc,christiaanb/ghc,green-haskell/ghc,siddhanathan/ghc,holzensp/ghc,nushio3/ghc,olsner/ghc,tjakway/ghcjvm,AlexanderPankiv/ghc,nkaretnikov/ghc,nathyong/microghc-ghc,holzensp/ghc,vikraman/ghc,ghc-android/ghc,jstolarek/ghc,AlexanderPankiv/ghc,lukexi/ghc,mcschroeder/ghc,shlevy/ghc,urbanslug/ghc,mcschroeder/ghc,da-x/ghc,snoyberg/ghc,hferreiro/replay,da-x/ghc,frantisekfarka/ghc-dsi,ghc-android/ghc,anton-dessiatov/ghc,ilyasergey/GHC-XAppFix,christiaanb/ghc,ghc-android/ghc,nomeata/ghc,ml9951/ghc,urbanslug/ghc,gcampax/ghc,nushio3/ghc,elieux/ghc,wxwxwwxxx/ghc,mfine/ghc,ezyang/ghc,vTurbine/ghc,tjakway/ghcjvm,TomMD/ghc,mfine/ghc,acowley/ghc,ghc-android/ghc,acowley/ghc,mettekou/ghc,anton-dessiatov/ghc,urbanslug/ghc,forked-upstream-packages-for-ghcjs/ghc,mcmaniac/ghc,sdiehl/ghc,AlexanderPankiv/ghc,ilyasergey/GHC-XAppFix,tibbe/ghc,ezyang/ghc,christiaanb/ghc,sgillespie/ghc,gcampax/ghc,nathyong/microghc-ghc,TomMD/ghc,GaloisInc/halvm-ghc,fmthoma/ghc,da-x/ghc,jstolarek/ghc,bitemyapp/ghc,olsner/ghc,siddhanathan/ghc,frantisekfarka/ghc-dsi,gcampax/ghc,mcmaniac/ghc,gridaphobe/ghc,sgillespie/ghc,vikraman/ghc,frantisekfarka/ghc-dsi,holzensp/ghc,elieux/ghc,hferreiro/replay,jstolarek/ghc,acowley/ghc,gcampax/ghc,da-x/ghc,vTurbine/ghc,ghc-android/ghc,ryantm/ghc,bitemyapp/ghc,anton-dessiatov/ghc,gridaphobe/ghc,AlexanderPankiv/ghc,snoyberg/ghc,fmthoma/ghc,christiaanb/ghc,urbanslug/ghc,oldmanmike/ghc,sdiehl/ghc,ekmett/ghc,mcmaniac/ghc,nkaretnikov/ghc,wxwxwwxxx/ghc,mcschroeder/ghc,mfine/ghc,bitemyapp/ghc,frantisekfarka/ghc-dsi,ryantm/ghc,TomMD/ghc,nkaretnikov/ghc,mcschroeder/ghc,nomeata/ghc,nathyong/microghc-ghc,olsner/ghc,olsner/ghc,urbanslug/ghc,hferreiro/replay,acowley/ghc,forked-upstream-packages-for-ghcjs/ghc,siddhanathan/ghc,ezyang/ghc,sgillespie/ghc,vikraman/ghc,holzensp/ghc,AlexanderPankiv/ghc,siddhanathan/ghc,vTurbine/ghc,frantisekfarka/ghc-dsi,snoyberg/ghc,sdiehl/ghc,ekmett/ghc,shlevy/ghc,siddhanathan/ghc,mettekou/ghc,ml9951/ghc,shlevy/ghc,oldmanmike/ghc,sgillespie/ghc,urbanslug/ghc,TomMD/ghc,ghc-android/ghc,wxwxwwxxx/ghc,tjakway/ghcjvm,anton-dessiatov/ghc,green-haskell/ghc,AlexanderPankiv/ghc,GaloisInc/halvm-ghc,mettekou/ghc,GaloisInc/halvm-ghc,lukexi/ghc,bitemyapp/ghc,wxwxwwxxx/ghc,anton-dessiatov/ghc,holzensp/ghc,shlevy/ghc