Gracefully handle channel bans and other join errors

http2irc.py

@@ -655,8 +655,12 @@ class IRCClientProtocol(asyncio.Protocol):
 		                      ircstates.numerics.ERR_BANNEDFROMCHAN,
 		                      ircstates.numerics.ERR_BADCHANNELKEY,
 		                     ):
-			self.logger.error(f'Failed to join channel: {message!r}, terminating connection')
-			self.transport.close()
+			self.logger.error(f'Failed to join channel {line.params[1]}: {message!r}')
+			errChannel = self.server.casefold(line.params[1])
+			for channel in self.channels:
+				if self.server.casefold(channel) == errChannel:
+					self.channels.remove(channel)
+					break
 
 		# PART errors
 		elif line.command == '442':