Null pointer reference if signals stacked on QComboBox

If 2 or more signals from QComboBox are connected to a slot (or slots) and the first slot to fire changes the combo box from editable to non-editable it causes a null pointer reference within the Qt libs.

I've attached a simplified example that reproduces the error. The example does not represent how things are being done in the real application, it's just an easy way to reproduce the crash.

Run the provided example and simply change the selected text within the combo box from "one" to "two" then back to "one". You don't need to edit the selected text when it goes editable, just change the selected text.