Don't track closed sessions with no path

spec/app/editor-spec.coffee

@@ -156,6 +156,9 @@ describe "Editor", ->
       editSession = editor.activeEditSession
       expect(editor.closedEditSessions.length).toBe 0
       editor.trigger "core:close"
+      expect(editor.closedEditSessions.length).toBe 0
+      editor.edit(rootView.project.buildEditSessionForPath(rootView.project.resolve('sample.txt')))
+      editor.trigger "core:close"
       expect(editor.closedEditSessions.length).toBe 1
 
     it "closes the active edit session and loads next edit session", ->

src/app/editor.coffee

@@ -492,7 +492,7 @@ class Editor extends View
     editSession = @editSessions[index]
     destroySession = =>
       path = editSession.getPath()
-      @closedEditSessions.push({path, index})
+      @closedEditSessions.push({path, index}) if path
       editSession.destroy()
       callback?(index)