BulkPurge NullReferenceException When Topic Has No Subscriptions

[avalanchis]

Summary:

Selecting any of the options under Topics -> Purge will cause a Null Reference Exception if a Topic exists with no Subscriptions.

Expected behavior:

1. Select Topics -> Purge -> Messages, Dead-letter Queue Messages, or All Messages
2. The appropriate purge function is performed on all topics.

Actual behavior:

1. Select Topics -> Purge -> Messages, Dead-letter Queue Messages, or All Messages

2. The following message appears in the Log window:

   <09:52:57> Exception: Object reference not set to an instance of an object.

[SeanFeldman]

Fixed via bc288d2