badblocks: avoid checking invalid range in badblocks_check()

If prev_badblocks() returns '-1', it means no valid badblocks record
before the checking range. It doesn't make sense to check whether
the input checking range is overlapped with the non-existed invalid
front range.

This patch checkes whether 'prev >= 0' is true before calling
overlap_front(), to void such invalid operations.

Fixes: 3ea3354c ("badblocks: improve badblocks_check() for multiple ranges handling")
Reported-and-tested-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Coly Li <colyli@suse.de>
Link: https://lore.kernel.org/nvdimm/3035e75a-9be0-4bc3-8d4a-6e52c207f277@leemhuis.info/
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Geliang Tang <geliang.tang@suse.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: NeilBrown <neilb@suse.de>
Cc: Vishal L Verma <vishal.l.verma@intel.com>
Cc: Xiao Ni <xni@redhat.com>
Link: https://lore.kernel.org/r/20231224002820.20234-1-colyli@suse.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>