Quoting multiple nonexistent messages results in channel spam + incorrect quote count.

[RalphORama]

Discovered during testing for the v1.0 release.

When you misquote a bunch of messages, as so:

QuoteBot spits out the following:

This bug is a twofer:

1. Condense No message exists with ID x error message.
2. Figure out why the continue on line 82 in quote.py doesn't actually continue.