Validator dialog crashes when the active edit layer is deleted

[Gnonthgol]

If you delete the active edit layer the validator dialog does not update. With some debuging I have found that the cause of the problem is that mapView.getActiveLayer() updates before the listeners are triggered. That causes the check at org.openstreetmap.josm.data.validation.OsmValidator:298 to fail every time.

Maybe it would be easier if the logic was moved to org.openstreetmap.josm.gui.dialogs.ValidatorDialog

[Don-vip]

Confirmed:

1. Download some data that produces validation warnings, and validate
2. Add Imagery layer
3. Delete edit layer
4. Select a primitive in validator dialog, which has not been updated:

   java.lang.NullPointerException
   	at org.openstreetmap.josm.gui.dialogs.ValidatorDialog.setSelectedItems(ValidatorDialog.java:369)
   	at org.openstreetmap.josm.gui.dialogs.ValidatorDialog.access$6(ValidatorDialog.java:347)
   	at org.openstreetmap.josm.gui.dialogs.ValidatorDialog$2.actionPerformed(ValidatorDialog.java:121)
   	at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
   	at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
   	at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
   	at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
   

[Don-vip]

In 5415/josm:

fix #7936 - Validator dialog is not updated when the active edit layer is deleted