[Azoth VB] Better code.
[Azoth VB] Return Protocol* directly from GetParentProtocol().

Covariant types are OK.
[Azoth VB] Store message more or less around sending it.
[Azoth VB] Check for inability to create convos or get buddy names.

Or, otherwise, check for libpurple crappiness :3

Rels to #1829.