Merge branch 'rs/c-auto-resets-attributes' into maint

When "%C(auto)" appears at the very beginning of the pretty format
string, it did not need to issue the reset sequence, but it did.
This is a small optimization to already graduated topic.

* rs/c-auto-resets-attributes:
  pretty: avoid adding reset for %C(auto) if output is empty
  pretty: let %C(auto) reset all attributes

pretty.c

@@ -1072,6 +1072,8 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 	case 'C':
 		if (starts_with(placeholder + 1, "(auto)")) {
 			c->auto_color = want_color(c->pretty_ctx->color);
+			if (c->auto_color && sb->len)
+				strbuf_addstr(sb, GIT_COLOR_RESET);
 			return 7; /* consumed 7 bytes, "C(auto)" */
 		} else {
 			int ret = parse_color(sb, placeholder, c);