Win32: fix detection of empty directories in is_dir_empty

On Windows XP (not Win7), directories cannot be deleted while a find handle
is open, causing "Deletion of directory '...' failed. Should I try again?"
prompts.

Prior to 19d1e75 "Win32: Unicode file name support (except dirent)",
these failures were silently ignored due to strbuf_free in is_dir_empty
resetting GetLastError to ERROR_SUCCESS.

Close the find handle in is_dir_empty so that git doesn't block deletion
of the directory even after all other applications have released it.

Reported-by: John Chen <[email protected]>
Signed-off-by: Karsten Blees <[email protected]>

Author: kblees

compat/mingw.c

@@ -241,8 +241,11 @@ static int is_dir_empty(const wchar_t *wpath)
 
 	while (!wcscmp(findbuf.cFileName, L".") ||
 			!wcscmp(findbuf.cFileName, L".."))
-		if (!FindNextFileW(handle, &findbuf))
-			return GetLastError() == ERROR_NO_MORE_FILES;
+		if (!FindNextFileW(handle, &findbuf)) {
+			DWORD err = GetLastError();
+			FindClose(handle);
+			return err == ERROR_NO_MORE_FILES;
+		}
 	FindClose(handle);
 	return 0;
 }