fixed GL nodes loader for maps loaded from mounted folders.

Due to how the reader  is created, READER_NEW will not work for it, it needs to force READER_CACHED.

src/maploader/glnodes.cpp

@@ -900,7 +900,8 @@ bool MapLoader::LoadGLNodes(MapData * map)
 					break;
 				}
 				else
-					gwalumps[i] = f_gwa->GetEntryReader(li + i + 1, FileSys::READER_NEW, FileSys::READERFLAG_SEEKABLE);
+					// This is a special case. The container for the map WAD is not set up to create new file handles for itself so this needs to cache the content here.
+					gwalumps[i] = f_gwa->GetEntryReader(li + i + 1, FileSys::READER_CACHED, FileSys::READERFLAG_SEEKABLE);
 			}
 			if (result) result = DoLoadGLNodes(gwalumps);
 		}