LibWeb: Set color filter value to 1 if omitted

Author: https://github.com/tcl3
Commit: 61f76c7ec5
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4222
Reviewed-by: https://github.com/AtkinsSJ ✅

Libraries/LibWeb/CSS/Parser/PropertyParsing.cpp

@@ -4433,7 +4433,7 @@ RefPtr<CSSStyleValue> Parser::parse_filter_value_list_value(TokenStream<Componen
                 if (amount->is_number() && amount->number().value() < 0)
                     return {};
             }
-            return if_no_more_tokens_return(FilterOperation::Color { filter_token_to_operation(filter_token), amount });
+            return if_no_more_tokens_return(FilterOperation::Color { filter_token_to_operation(filter_token), amount.value_or(Number { Number::Type::Integer, 1 }) });
         }
     };