<karlt@karlt.net> to fix dosfsck zero slot crashes:
* Fixes crashes due to zero slot numbers causing a negative offset in
the call to copy_lfn_part in lfn_add_slot. On amd64 this results in
a SIGSEGV in copy_lfn_part. On x86 the result is heap corruption and
thus sometimes a SIGSEGV or double free abort later. (Closes:
#152550, #353198, #356377, #401798).
Signed-off-by: Daniel Baumann <mail@daniel-baumann.ch>
