[krbdev.mit.edu #7900] Seg fault when principal key cannot be read

[Robin McCorkell via RT]

I have found a segmentation fault situation, where the principal key is
assumed to be readable (and thus the required data structures have been
populated).

The offending line is line 451 of src/lib/kdb/kdb_default.c:

    if (mkey->enctype == master_entry->key_data[0].key_data_type[0]) {

In the case of an incorrectly configured LDAP directory for example,
this seg faults the KDC on start up, as master_entry->key_data is still
set to NULL.