Fix a conversion warning in the mingw32 build

gcc diagnoses this:
  warning: converting to non-pointer type 'unsigned int' from NULL

Also remove an empty statement.

No change in functionality.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192955 91177308-0d34-0410-b5e6-96231b3b80d8