Fix bug: Don't call handleKeyEvent with undefined event

Ace triggers key handlers for both keydown (onCommandKey) and input
(onTextInput) events. Input events don't pass the event, which was
blowing up the keymap.

src/atom/editor.coffee

@@ -35,10 +35,9 @@ class Editor extends Template
     buildAceEditor: ->
       @aceEditor = ace.edit this[0]
       @aceEditor.setTheme(require "ace/theme/twilight")
-
       @aceEditor.setKeyboardHandler
-        handleKeyboard: (data, hashId, keyString, keyCode, e) =>
-          if @keyEventHandler?.handleKeyEvent(e)
+        handleKeyboard: (data, hashId, keyString, keyCode, event) =>
+          if event and @keyEventHandler?.handleKeyEvent(event)
             {command: {exec: ->}}
           else
             null