Fix MinecraftChannelIdentifier parsing to align with vanilla

[booky10]

As of 163a85a, Velocity will attempt to parse all custom payload channels registered/unregistered by clients and kick the client if it appears to be "invalid".
Because of this change, some minor differences between vanilla's ResourceLocation and Velocity's MinecraftChannelIdentifier caused players using certain mods to be kicked on login.

This PR fixes the parsing of MinecraftChannelIdentifier to match vanilla.

[electronicboy]

Thanks, but, I'm generally somewhat iffy on the nature of allowing purely namespace keys, though, I did forget to potentially add skipping of empty strings to mitigate some forge oddities on server switching

[booky10]

Thanks, but, I'm generally somewhat iffy on the nature of allowing purely namespace keys, though, I did forget to potentially add skipping of empty strings to mitigate some forge oddities on server switching

I think the issue you are referring to is forge always appending an extra null byte to their channel-register packet

Ignoring empty channel names in plugin message packets sounds good, but I would still argue that Velocity should try to keep the same logic as vanilla and allow parsing empty strings as MinecraftChannelIdentifier for as long as vanilla allows this too