10306 mdb: NULL pointer errors
Reviewed by: Robert Mustacchi <rm@joyent.com>
Reviewed by: Gergő Mihály Doma <domag02@gmail.com>
Approved by: Dan McDonald <danmcd@joyent.com>

7299 want dnlc walker for mdb
Reviewed by: Jerry Jelinek <jerry.jelinek@joyent.com>
Reviewed by: Gordon Ross <gordon.w.ross@gmail.com>
Approved by: Richard Lowe <richlowe@richlowe.net>