parser: Fix parsing of Retry-After header

- Allow no space between duration and optional comment

(cherry picked from commit accfbe0abb0d811e249b687cb6047c9234a6d884)
(cherry picked from commit f66d5efb20e5acec87c8b9d38a9a6c5faacc4a18)

parser/parse_retry_after.c

@@ -59,6 +59,7 @@ char* parse_retry_after(char* const buf, const char* const end, unsigned* const
 				case ';':
 				case '\r':
 				case '\n':
+				case '(':
 					goto found;
 				default:
 					/* invalid char */