LibPDF: Avoid unnecessary HashMap copy, mark other copies

Author: https://github.com/BenWiederhake
Commit: f866c80222
Pull-request: https://github.com/SerenityOS/serenity/pull/18821
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/gmta ✅
Reviewed-by: https://github.com/kleinesfilmroellchen ✅

Userland/Libraries/LibPDF/Parser.cpp

@@ -432,7 +432,7 @@ PDFErrorOr<NonnullRefPtr<DictObject>> Parser::parse_dict()
         return error("Expected dict to end with \">>\"");
     m_reader.consume_whitespace();
 
-    return make_object<DictObject>(map);
+    return make_object<DictObject>(move(map));
 }
 
 PDFErrorOr<NonnullRefPtr<StreamObject>> Parser::parse_stream(NonnullRefPtr<DictObject> dict)