fix error when open project and close editor
### when open project ###
```
ERROR: Attempt to connect nonexistent signal 'size_flags_changed' to method 'queue_sort'
At: core\object.cpp:1400
ERROR: Attempt to connect nonexistent signal 'minimum_size_changed' to method '_child_minsize_changed'
At: core\object.cpp:1400
ERROR: Attempt to connect nonexistent signal 'visibility_changed' to method '_child_minsize_changed'
At: core\object.cpp:1400
```
### when close editor ###
```
ERROR: Nonexistent signal: size_flags_changed
At: core\object.cpp:1458
ERROR: Nonexistent signal: minimum_size_changed
At: core\object.cpp:1458
ERROR: Nonexistent signal: visibility_changed
At: core\object.cpp:1458
```