Ignore approvals without descriptions

We don't really offer a facility to match on non-review category
approvals (like SUBM) so ignore those when matching events to
triggers.  Otherwise, matching logic that expects only review
categories will be fooled by submit or other similar approval
types.

Fixes-bug: 1284842
Fixes-bug: 1285210

Change-Id: I68b58f611df8fc2b9b2753d1579eae2e6898acc9