LWSImporter: Fix direct memory leak

- Fix leak found by fuzzer
- closes https://github.com/assimp/assimp/issues/4231

code/AssetLib/LWS/LWSLoader.cpp

@@ -927,6 +927,7 @@ void LWSImporter::InternReadFile(const std::string &pFile, aiScene *pScene, IOSy
             SkeletonMeshBuilder builder(pScene);
         }
     }
+    delete master;
 }
 
 #endif // !! ASSIMP_BUILD_NO_LWS_IMPORTER