Don't assert on invalid 0-bytes palettes (no user strings)
Before this commit, Krita would assert when the palette stored in .kra file was 0-bytes. While it is an incorrect situation, Krita shouldn't crash/assert, but inform the user about it and load the rest of the file. Cherry-picked from fbc005b1, but without the new user string.
Showing with 6 additions and 5 deletions