erofs: relax sanity check for tail pclusters due to ztailpacking

erofs: relax sanity check for tail pclusters due to ztailpacking

If the tail data can be inlined into the inode meta block, it should
be converted into a regular tail pcluster.

In principle, it should be converted into an uncompressed pcluster if
there is not enough gain to use compression (map->m_llen < map->m_plen);
but since there are various shipped images, relax the condition for
ztailpacking tail pcluster fallback instead of reporting corruption
incorrectly.

Reported-and-tested-by: Yifan Zhao <zhaoyifan28@huawei.com>
Reported-by: Alberto Salvia Novella <es20490446e@gmail.com>
Closes: https://github.com/erofs/erofs-utils/issues/51
Fixes: a5242d37c83a ("erofs: error out obviously illegal extents in advance")
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>