Don't freak when selections are added & removed before display update

Previously, if a selection was added and removed before the editor got
a chance to update its display, it would try to add a selection view
for the destroyed selection. Now we check the new selections and
cursors to make sure they aren't destroyed before we add views for
them.

spec/app/editor-spec.coffee

@@ -765,6 +765,18 @@ describe "Editor", ->
         expect(editor.getSelectionViews().length).toBe 1
         expect(editor.find('.region').length).toBe 3
 
+    describe "when a selection is added and removed before the display is updated", ->
+      it "does not attempt to render the selection", ->
+        # don't update display until we request it
+        jasmine.unspy(editor, 'requestDisplayUpdate')
+        spyOn(editor, 'requestDisplayUpdate')
+
+        editSession = editor.activeEditSession
+        selection = editSession.addSelectionForBufferRange([[3, 0], [3, 4]])
+        selection.destroy()
+        editor.updateDisplay()
+        expect(editor.getSelectionViews().length).toBe 1
+
     describe "when the selection is created with the selectAll event", ->
       it "does not scroll to the end of the buffer", ->
         editor.height(150)

src/app/cursor.coffee

@@ -34,6 +34,7 @@ class Cursor
     @needsAutoscroll = true
 
   destroy: ->
+    @destroyed = true
     @editSession.destroyMarker(@marker)
     @editSession.removeCursor(this)
     @trigger 'destroyed'

src/app/editor.coffee

@@ -780,7 +780,7 @@ class Editor extends View
 
   updateCursorViews: ->
     if @newCursors.length > 0
-      @addCursorView(cursor) for cursor in @newCursors
+      @addCursorView(cursor) for cursor in @newCursors when not cursor.destroyed
       @syncCursorAnimations()
       @newCursors = []
 
@@ -792,7 +792,7 @@ class Editor extends View
 
   updateSelectionViews: ->
     if @newSelections.length > 0
-      @addSelectionView(selection) for selection in @newSelections
+      @addSelectionView(selection) for selection in @newSelections when not selection.destroyed
       @newSelections = []
 
     for selectionView in @getSelectionViews()