Ensure connection is active before initializing addon

[MelanX]

In some cases, a connection may not have any channel. In this case, ChannelAttributes.getOrCreateCommonChannels shouldn't be called because it creates a NullPointerException. If the channel is null, it should just not continue with collecting channels and initializing it for the addon.

Maybe, we should also not check isConnected but instead isConnecting since isConnected also checks for Channel#isOpen and isConnecting only checks if channel is null.