LibWeb/CSS: Don't overwrite active font load when requesting a pt size

start_loading_next_url() is a no-op if there's a pending resource load,
but not if that resource load has successfully loaded already. There is
a delay between the font resource loading, and it being processed into
a vector font. Calling font_with_point_size() in that gap would
previously erase the previously-loaded font, if the font had multiple
URLs to choose from.

This fixes the icon font on mods.factorio.com :^)

(cherry picked from commit 28388f1fd24c0019d2c4be7900584c6c536527ad)

Userland/Libraries/LibWeb/CSS/StyleComputer.cpp

@@ -170,7 +170,8 @@ void FontLoader::resource_did_fail()
 RefPtr<Gfx::Font> FontLoader::font_with_point_size(float point_size)
 {
     if (!m_vector_font) {
-        start_loading_next_url();
+        if (!resource())
+            start_loading_next_url();
         return nullptr;
     }
     return m_vector_font->scaled_font(point_size);