Fix: Fix leak in Scope class, FBX

- closes https://github.com/assimp/assimp/issues/3421

code/AssetLib/FBX/FBXParser.cpp

@@ -188,15 +188,19 @@ Scope::Scope(Parser& parser,bool topLevel)
             ParseError("unexpected content: empty string.");
         }
 
-        elements.insert(ElementMap::value_type(str,new_Element(*n,parser)));
+        auto *element = new_Element(*n, parser);
         
         // Element() should stop at the next Key token (or right after a Close token)
         n = parser.CurrentToken();
         if (n == nullptr) {
             if (topLevel) {
+                elements.insert(ElementMap::value_type(str, element));
                 return;
             }
             ParseError("unexpected end of file",parser.LastToken());
+            delete element;
+        } else {
+            elements.insert(ElementMap::value_type(str, element));
         }
     }
 }