prevent delete-track-undo from crashing if previously connected jack connection quit in the meantime

template/engine/sequencer.py

@@ -390,7 +390,10 @@ class SequencerInterface(_Interface): #Basically the midi part of a track.
         cbox.JackIO.rename_midi_output(self.cboxMidiOutUuid, self._name)
         self.calfboxTrack.set_external_output(self.cboxMidiOutUuid)
         for port in self._beforeDeleteThisJackMidiWasConnectedTo:
+            try:
                 cbox.JackIO.port_connect(self.cboxPortName(), port)
+            except: #external connected synth is maybe gone. Prevent crash.
+                logger.warning(f"Previously external connection {port} is gone. Can't connect anymore." )
 
         #Make it official
         self._updatePlayback()