After closing a workspace, you cannot open any jar/class by dragging it.

[Tom Xin]

Describe the bug

Some exceptions are thrown after closing the workspace, and the workspace cannot be opened by dragging files until Recaf is restarted

To Reproduce

Steps to reproduce the behavior:

1. Open any jar/class by Reacf

2. Close the workspace by File -> Close.At this time, the Logging window of Recaf will display Exception thrown when closing workspace
   

3. Drag any jar/class file to the Recaf window and it cannot be opened
   

Exception
java.lang.NullPointerException: 'workspace' must not be null
Log
log-2024-06-06.txt

Screenshots

[Matt]

47ee102 - Made a copy/paste bug when updating listeners recently. Fixed now.