avfilter/vf_mestimate: Check b_count

Fixes: left shift of negative value -1
Fixes: Ticket8270

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 06af6e101b)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
This commit is contained in:
Michael Niedermayer 2021-06-05 20:04:45 +02:00
parent fb7379f7ef
commit 6ce4989432