patches: move assignment outside the conditional

patches: move assignment outside the conditional

Having this movement in its own patch will make the next patch clearer.

--- a/mercurial/cext/mpatch.c	Sun Feb 04 14:58:32 2018 -0800
+++ b/mercurial/cext/mpatch.c	Tue Feb 06 14:24:16 2018 +0100
@@ -110,7 +110,8 @@
 		goto cleanup;
 	}
 	out = PyBytes_AsString(result);
-	if ((r = mpatch_apply(out, in, inlen, patch)) < 0) {
+	r = mpatch_apply(out, in, inlen, patch);
+	if (r < 0) {
 		Py_DECREF(result);
 		result = NULL;
 	}