Slightly simplify the Catalog._readMarkInfo method

We don't need to first check if the Dictionary contains the key, since trying to get a non-existent key simply returns `undefined` and we're already ensuring that the value is a boolean.
Furthermore, we shouldn't need to worry about the `Object.prototype` containing enumerable properties since the checks (in `src/core/worker.js`) done for `Array.prototype` *indirectly* also cover `Object`s. (Keep in mind that an `Array` is just a special kind of `Object` in JavaScript.)

src/core/catalog.js

@@ -209,20 +209,16 @@ class Catalog {
       return null;
     }
 
-    const markInfo = Object.assign(Object.create(null), {
+    const markInfo = {
       Marked: false,
       UserProperties: false,
       Suspects: false,
-    });
+    };
     for (const key in markInfo) {
-      if (!obj.has(key)) {
-        continue;
-      }
       const value = obj.get(key);
-      if (typeof value !== "boolean") {
-        continue;
+      if (typeof value === "boolean") {
+        markInfo[key] = value;
       }
-      markInfo[key] = value;
     }
 
     return markInfo;