Add a workaround for loading broken files with negative frame ids
Summary: CCBUG:395378
Test Plan:
Try to load the file attached to this bugreport:
https://bugs.kde.org/show_bug.cgi?id=395378
Every layer in the file should have two frames (in random order). At least one
of the frames should have sane pixel data
Reviewers: Krita, rempt, jounip
Tags: Krita
Differential Revision: https://phabricator.kde.org/D13562