Do not try to get Git revision in `git.rev_parse` if the directory is not a repo.
Do not try to get Git revision in `git.rev_parse` if the directory is not a repo.

mohtamohit/CppSharp,ddobrev/CppSharp,mohtamohit/CppSharp,mono/CppSharp,ddobrev/CppSharp,mono/CppSharp,mohtamohit/CppSharp,zillemarco/CppSharp,zillemarco/CppSharp,ddobrev/CppSharp,zillemarco/CppSharp,mono/CppSharp,zillemarco/CppSharp,mono/CppSharp,ddobrev/CppSharp,mono/CppSharp,zillemarco/CppSharp,ddobrev/CppSharp,mohtamohit/CppSharp,mohtamohit/CppSharp,mono/CppSharp