diff: avoid some nesting

Avoid some nesting in builtin/diff.c, to make the code easier to read.
There are no functional changes.

Helped-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/diff.c

@@ -319,8 +319,7 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 
 	init_revisions(&rev, prefix);
 
-	if (no_index) {
+	if (no_index && argc != i + 2) {
-		if (argc != i + 2) {
 		if (no_index == DIFF_NO_INDEX_IMPLICIT) {
 			/*
 			 * There was no --no-index and there were not two
@@ -337,9 +336,9 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 		       "--no-index" : "[--no-index]");
 
 	}
+	if (no_index)
 		/* If this is a no-index diff, just run it and exit there. */
 		diff_no_index(&rev, argc, argv, prefix);
-	}
 
 	/* Otherwise, we are doing the usual "git" diff */
 	rev.diffopt.skip_stat_unmatch = !!diff_auto_refresh_index;