Handle deleted files semi-gracefully

services/web/public/coffee/file-tree/FileTreeManager.coffee

@@ -97,7 +97,7 @@ define [
 				@views[@selected_entity_id].deselect()
 			@selected_entity_id = entity_id
 			@ide.sideBarView.deselectAll()
-			@views[entity_id].select()
+			@views[entity_id]?.select()
 
 		getEntity: (entity_id) ->
 			@views[entity_id]?.model

services/web/public/coffee/track-changes/TrackChangesManager.coffee

@@ -127,6 +127,10 @@ define [
 			if @diffView?
 				@diffView.remove()
 
+			if !@diff.get("doc")?
+				console.log "This document has been deleted. What should we do?"
+				return
+
 			@diffView = new DiffView(
 				model: @diff
 				el:    @$el.find(".track-changes-diff")