GIMP could crash if the information regarding old path properties read
from XCF was incorrect. It did not check if xcf_old_path succeeded and
kept trying to load more paths even if the last one failed to load.

Instead we now stop loading paths as soon as that function fails.
In case we have a failure here we also try to skip to the next property
based on the size of the path property, in hopes that the only problem
was this property.

(cherry picked from commit 4f99f1fc)