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

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.

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

pretty.c

@@ -1072,7 +1072,7 @@ 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)
+			if (c->auto_color && sb->len)
 				strbuf_addstr(sb, GIT_COLOR_RESET);
 			return 7; /* consumed 7 bytes, "C(auto)" */
 		} else {

t/t6006-rev-list-format.sh

@@ -225,7 +225,7 @@ test_expect_success '%C(auto,...) respects --color=auto (stdout not tty)' '
 
 test_expect_success '%C(auto) respects --color' '
 	git log --color --format="%C(auto)%H" -1 >actual &&
-	printf "\\033[m\\033[33m%s\\033[m\\n" $(git rev-parse HEAD) >expect &&
+	printf "\\033[33m%s\\033[m\\n" $(git rev-parse HEAD) >expect &&
 	test_cmp expect actual
 '