Fix hang when utf line break is used

Break the loop: if adding an offset to the number of columns doesn't
increase the line length, we break out of the loop to avoid an
infinite loop on loading some files.

Shift + Enter creates an utf break character which breaks
the lenght calculation. Also added a reptition flag to avoid
any other hang if there is a strange symbol.

BUG:410402

ref:https://invent.kde.org/kde/krita/merge_requests/128

(cherry picked from commit 535ca1fc6fde92003258c2dd861e05cce3bf8004)