git-status -v: color diff output when color.ui is set

When using "git status -v", the diff output wasn't colored, even though
color.ui was set. Only when setting color.diff it worked.

Signed-off-by: Markus Heidelberg <markus.heidelberg@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-commit.c

@@ -866,6 +866,9 @@ int cmd_status(int argc, const char **argv, const char *prefix)
 	if (wt_status_use_color == -1)
 		wt_status_use_color = git_use_color_default;
 
+	if (diff_use_color_default == -1)
+		diff_use_color_default = git_use_color_default;
+
 	argc = parse_and_validate_options(argc, argv, builtin_status_usage, prefix);
 
 	index_file = prepare_index(argc, argv, prefix);