qcow2: Move error check of local_err near its assignment

qcow2: Move error check of local_err near its assignment

The local_err check outside of the if block was necessary
when it was introduced in commit d1258dd0c87 because it needed to be
executed even if qcow2_load_autoloading_dirty_bitmaps() returned false.

After some modifications that all required the error check to remain
where it is, commit 9c98f145dfb finally moved the
qcow2_load_dirty_bitmaps() call into the if block, so now the error
check should be there, too.

Signed-off-by: Guoyi Tu <tu.guoyi@h3c.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>