patch 8.1.0601: a few compiler warnings

Problem:    A few compiler warnings.
Solution:   Add type casts. (Mike Williams)

src/GvimExt/gvimext.cpp

@@ -1084,7 +1084,6 @@ STDMETHODIMP CShellExt::InvokeSingleGvim(HWND hParent,
 	CloseHandle(pi.hProcess);
 	CloseHandle(pi.hThread);
     }
-theend:
     free(cmdStrW);
 
     return NOERROR;