Handle editor destruction when dragging.

Closes #4622

spec/text-editor-component-spec.coffee

@@ -1612,6 +1612,22 @@ describe "TextEditorComponent", ->
         expect(nextAnimationFrame).toBe noAnimationFrame
         expect(editor.getSelectedScreenRange()).toEqual [[2, 4], [6, 8]]
 
+      describe "when the editor is destroyed while dragging", ->
+        it "cleans up the handlers for window.mouseup and window.mousemove", ->
+          linesNode.dispatchEvent(buildMouseEvent('mousedown', clientCoordinatesForScreenPosition([2, 4]), which: 1))
+          linesNode.dispatchEvent(buildMouseEvent('mousemove', clientCoordinatesForScreenPosition([6, 8]), which: 1))
+          nextAnimationFrame()
+
+          spyOn(window, 'removeEventListener').andCallThrough()
+
+          linesNode.dispatchEvent(buildMouseEvent('mousemove', clientCoordinatesForScreenPosition([6, 10]), which: 1))
+          editor.destroy()
+          nextAnimationFrame()
+
+          call.args.pop() for call in window.removeEventListener.calls
+          expect(window.removeEventListener).toHaveBeenCalledWith('mouseup')
+          expect(window.removeEventListener).toHaveBeenCalledWith('mousemove')
+
     describe "when a line is folded", ->
       beforeEach ->
         editor.foldBufferRow 4

src/text-editor-component.coffee

@@ -750,10 +750,12 @@ TextEditorComponent = React.createClass
     lastMousePosition = {}
     animationLoop = =>
       @requestAnimationFrame =>
-        if dragging
+        if dragging and @isMounted()
           screenPosition = @screenPositionForMouseEvent(lastMousePosition)
           dragHandler(screenPosition)
           animationLoop()
+        else if not @isMounted()
+          stopDragging()
 
     onMouseMove = (event) ->
       lastMousePosition.clientX = event.clientX
@@ -768,10 +770,13 @@ TextEditorComponent = React.createClass
       onMouseUp() if event.which is 0
 
     onMouseUp = ->
+      stopDragging()
+      editor.finalizeSelections()
+
+    stopDragging = ->
       dragging = false
       window.removeEventListener('mousemove', onMouseMove)
       window.removeEventListener('mouseup', onMouseUp)
-      editor.finalizeSelections()
 
     window.addEventListener('mousemove', onMouseMove)
     window.addEventListener('mouseup', onMouseUp)