LibWeb: Fix regression of "contenteditable" attribute

Author: https://github.com/SeekingBlues
Commit: 08359ba578
Pull-request: https://github.com/SerenityOS/serenity/pull/9125
Reviewed-by: https://github.com/awesomekling

Userland/Libraries/LibWeb/HTML/Parser/HTMLToken.h

@@ -40,9 +40,9 @@ public:
 
     struct Attribute {
         String prefix;
-        String local_name;
+        String local_name { "" };
         String namespace_;
-        String value;
+        String value { "" };
         Position name_start_position;
         Position value_start_position;
         Position name_end_position;