mpatch: silence warning about maybe-uninitialized variable

It's false positive, but it wouldn't be possible for gcc to know
PyBytes_FromStringAndSize() sets PyErr_Occurred().

  mercurial/mpatch_module.c:105:47: warning: 'r' may be used uninitialized
  in this function [-Wmaybe-uninitialized]
     PyErr_SetString(mpatch_Error, mpatch_errors[-r]);

mercurial/mpatch_module.c

@@ -59,7 +59,7 b' patches(PyObject *self, PyObject *args)'
 	PyObject *text, *bins, *result;
 	struct mpatch_flist *patch;
 	const char *in;
-	int r;
+	int r = 0;
 	char *out;
 	Py_ssize_t len, outlen, inlen;