Fix crash in Dolphin when dropping trashed file in trash. The actual
crash happens because of an assertion failure in kcoredirlister_p.h:308
and this is triggered from kcoredirlister.cpp:995. What actually happens
is that the dropjob determines that it should perform a move action
which ends up being a rename operation for kio_trash. But it ends up
moving the file to itself and this triggers the above crash. The
solution is to error out in the dropjob with a KIO::ERR_DROP_ON_ITSELF
error so that the user can see that it doesn't make sense to drop a
file from the trash inside the trash again.
BUG: 378051