Endless state transition guard

Summary:
This e.g. catches the "hang" people did see before the fix in https://phabricator.kde.org/D15773
Its a simple good old "endless loop counter" that aborts after too many transitions.
IMHO more than a few without any progress at the text offset make no sense, therefore the hard limit of 1024 should be reasonable

Test Plan:
I tried the examples attached for https://phabricator.kde.org/D15773, with my fix, I get just

Endless state transitions, aborting highlighting of line.

as debug output but no longer any hang.

(but yes, the highlighting of some lines is messed up, which IMHO is ok, much better than a hard hang of the application

Reviewers: dhaumann, vkrause, nibags

Reviewed By: vkrause

Subscribers: kwrite-devel, kde-frameworks-devel

Tags: Kate, Frameworks

Differential Revision: https://phabricator.kde.org/D15836