[KComboBox] fix crash when calling setEditable(false) with open context menu
requested to merge pdabrowski/kcompletion:phd-KComboBox-contextmenu-setEditable-crash-fix into master
[KComboBox]
Fix crash when calling setEditable(false) with open context menu, and then closing the menu.
Also export contextMenu() so that users can handle open context menu themselves.
Edited by Piotr Henryk Dabrowski