check file existence before removing it
check file existence before removing it

This is an attempt to resolve an issue with warnings being thrown by
hhvm.

theUniC/Stash,csburton/Stash,jaredtking/Stash,andrerom/Stash,AndrewCarterUK/Stash,theUniC/Stash,tedious/Stash,tedious/Stash,alawnchen/Stash,AndrewCarterUK/Stash,alawnchen/Stash,graphis/Stash,graphis/Stash,jaredtking/Stash,csburton/Stash,bankiru/Stash,localheinz/Stash,localheinz/Stash,andrerom/Stash,bankiru/Stash