This fixes an issue that makes drag and drop sometimes not work.
Steps to reproduce:
Desired behavior: As long as the cursor is within the window-close area the cursor should indicate that dropping is allowed.
Actual behavior: As soon as the cursor enters the area where the panel usually is visible the cursor changes to indicate that dropping is not allowed.
Disclaimer: this is a small fix that may have wide-reaching implications. The fix should be thoroughly tested in different drag-and-drop scenarios.
[DND] Only pick reactive actors as drop targets.
Better close this before it starts to rot.