qemu-img: fix division by zero in bench_cb() for zero-sized images

qemu-img: fix division by zero in bench_cb() for zero-sized images

This error was discovered by fuzzing qemu-img.

This commit fixes a division by zero error in the bench_cb() function
that occurs when using the bench command with a zero-sized image.

The issue arises because b->image_size can be zero, leading to a
division by zero in the modulo operation (b->offset %= b->image_size).
This patch adds a check for b->image_size == 0 and resets b->offset
to 0 in such cases, preventing the error.

Signed-off-by: Denis Rastyogin <gerben@altlinux.org>
Message-ID: <20250318101933.255617-1-gerben@altlinux.org>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>