Various issues when choosing inactive option in context menu

[Piotrek Koszuliński]

1. Open replacebyclass sample.
2. Place caret in table cell.
3. Press "option key" or click right mouse button to open context menu.
4. Using keyboard navigate to Cell -> Merge cells (which is disabled).
5. Press enter or click that option.

General problem - nothing should happen IMO when choosing disabled option.

Browser specific:

• IE: focus is completely lost - I'm unable to close the context menu or navigate in it.
• Chrome: focus is lost (at least I think so, because none option is focused), but everything still works.

[Jakub Ś]

I see two issues here.

After selecting inactive menu option, menu was closed. It was happening till CKE 3.6.1 rev. [6920]. With this revision it was fixed incompletely.

• IE - focus is lost and this issue can be reproduced from CKEditor 3.6.1 rev. [6920].
• Chrome - it was working fine from CKE 3.6.1 till CKE 3.6.6 and got broken in CKE 4.0 beta. Actually only visible selection is lost. If after pressing enter you press down arrow, focus will show up on next menu element.

[Jakub Ś]

Could be related to #11501