SpMorphicBoxAdapter>>#remove: can crash

[jecisc]

In Pharo CI we have a lot of crashes due to rendering errors. Recently we removed an #on:do: that was preventing us to get the debug stack logged and we found out that one place we get this error is in SpMorphicBoxAdapter.

#widget was sent to nil
UndefinedObject(Object)>>doesNotUnderstand: #widget
SpMorphicBoxAdapter>>remove:
[ :ann |
		self remove: ann child ] in SpMorphicBoxAdapter>>layout: in Block: [ :ann |...
FullBlockClosure(BlockClosure)>>cull:
FullBlockClosure(BlockClosure)>>cull:cull:
[ action cull: anAnnouncement cull: announcer ] inAnnouncementSubscription(AbstractAnnouncementSubscription)>>deliver:in Block: [ action cull: anAnnouncement cull: announcer ]
FullBlockClosure(BlockClosure)>>on:do:
[ Processor terminateRealActive ] in [ :ex |
			  | onDoCtx handler bottom thisCtx |
			  onDoCtx := thisContext.
			  thisCtx := onDoCtx home.

			  "find the context on stack for which this method's is sender"
			  [ onDoCtx sender == thisCtx ] whileFalse: [
				  onDoCtx := onDoCtx sender.
				  onDoCtx ifNil: [ "Can't find our home context. seems like we're already forked
				and handling another exception in new thread. In this case, just pass it through handler."
					  ^ handlerAction cull: ex ] ].

			  bottom := [ Processor terminateRealActive ] asContext.
			  onDoCtx privSender: bottom.
			  handler := [ handlerAction cull: ex ] asContext.
			  handler privSender: thisContext sender.

			  (Process forContext: handler priority: Processor activePriority) resume.
			  "cut the stack of current process"
			  thisContext privSender: thisCtx.
			  nil ] in FullBlockClosure(BlockClosure)>>on:fork: in Block: [ Processor terminateRealActive ]