Unable to hash block devices

[simsong]

Converted from SourceForge issue 3586365, submitted by jessekornblum

After version 3.9.2, the programs produce NULL hashes for block devices. Here's a sample of hashing a block device, first with version 3.9.2, and then with version 4.3. Notice the second hash is equivalent to the null hash:

$ ./md5deep/md5deep -v
3.9.2
$ sudo ./md5deep/md5deep -e /dev/rdisk1
6eda1b68ef9d4f50bbab007a437e9b72 /dev/rdisk1

$ md5deep -v
4.3
$ sudo md5deep -e /dev/rdisk1
d41d8cd98f00b204e9800998ecf8427e /dev/rdisk1
$ md5deep /dev/null
d41d8cd98f00b204e9800998ecf8427e /dev/null