e2fsprogs: fix blkid whole-disk scanning heuristics

e2fsprogs: fix blkid whole-disk scanning heuristics

The heuristics in blkid/devname.c probe_all() for scanning whole disks
with no partitions assume that a device name with no digit on the end
will always be present as a delineator, i.e.:

sda
sda1
sdb
sdc

In this case, when sdc is seen, it's the clue to go back and scan sdb.
However, for something like:

sda
sda1
sdb
loop0

this falls down, and sdb is never scanned.
(thanks to Karel Zak for pointing this out).

Addresses-Red-Hat-Bugzilla: #400321

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>