btrfs-progs: check: lowmem: Fix extent item size false alert

btrfs-progs: check: lowmem: Fix extent item size false alert

If one extent item has no inline ref, btrfs lowmem mode check can give
false alert without outputting any error message.

The problem is lowmem mode always assumes that extent item has inline
refs, and when it encounters such case it flags the extent item has
wrong size, but doesn't output the error message.

Although we already have such image submitted, at the commit time due to
another bug in cmds-check return value, it doesn't detect it until that
bug is fixed.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>