stop spurious cancels

lib/view-model.coffee

@@ -7,12 +7,16 @@ class ViewModel
     @view = new ExCommandModeInputElement().initialize(@, opts)
     @editor.commandModeInputView = @view
     @exState.onDidFailToExecute => @view.remove()
+    @done = false
 
   confirm: (view) ->
     @exState.pushOperations(new Input(@view.value))
+    @done = true
 
   cancel: (view) ->
-    @exState.pushOperations(new Input(''))
+    unless @done
+      @exState.pushOperations(new Input(''))
+      @done = true
 
 class Input
   constructor: (@characters) ->