Fix crash when closing editors via vim command.

With a split view open (:sp) closing the split
editor (:on) would crash.

Change-Id: I85defb6b9d3e1d63a524eab5ebf2be368d8ccc33
Reviewed-by: hjk <hjk121@nokiamail.com>

src/plugins/fakevim/fakevimhandler.cpp

@@ -5335,6 +5335,11 @@ void FakeVimHandler::Private::handleExCommand(const QString &line0)
         }
         lastCommand = line;
     }
+
+    // if the last command closed the editor, we would crash here (:vs and then :on)
+    if (!(m_textedit || m_plaintextedit))
+        return;
+
     endEditBlock();
 
     resetCommandMode();