LibRegex: Disallow unescaped quantifiers in Unicode mode

Author: https://github.com/trflynn89
Commit: 1a173be29d
Pull-request: https://github.com/SerenityOS/serenity/pull/9367
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibRegex/RegexParser.cpp

@@ -1290,6 +1290,9 @@ bool ECMA262Parser::parse_atom(ByteCode& stack, size_t& match_length_minimum, bo
     }
 
     if (match(TokenType::RightBracket) || match(TokenType::RightCurly) || match(TokenType::LeftCurly)) {
+        if (unicode)
+            return set_error(Error::InvalidPattern);
+
         if (m_should_use_browser_extended_grammar) {
             auto token = consume();
             match_length_minimum += 1;