LibWeb/CSS: Don't allow negative border radius in box-shadow property

Author: https://github.com/tcl3
Commit: 632fc73643
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3916
Reviewed-by: https://github.com/AtkinsSJ ✅

Libraries/LibWeb/CSS/Parser/PropertyParsing.cpp

@@ -1816,6 +1816,10 @@ RefPtr<CSSStyleValue> Parser::parse_single_shadow_value(TokenStream<ComponentVal
             if (!maybe_blur_radius)
                 continue;
             blur_radius = maybe_blur_radius;
+            if (blur_radius->is_length() && blur_radius->as_length().length().raw_value() < 0)
+                return nullptr;
+            if (blur_radius->is_percentage() && blur_radius->as_percentage().value() < 0)
+                return nullptr;
             tokens.discard_a_token();
 
             // spread distance (optional)