LibWeb: VERIFY that nobody tries to hash a non-finite CSSPixels value

Non-finite CSSPixels quantities should never make their way into hash
tables. If this ever happens, let's catch it closer to the source
instead of letting things cascade into confusion.

Userland/Libraries/LibWeb/PixelUnits.h

@@ -127,6 +127,7 @@ template<>
 struct Traits<Web::CSSPixels> : public GenericTraits<Web::CSSPixels> {
     static unsigned hash(Web::CSSPixels const& key)
     {
+        VERIFY(isfinite(key.value()));
         return Traits<Web::CSSPixels::Type>::hash(key.value());
     }