Fix for an exploit with built-in plugin channels that induces lag/crashes. (BUKKIT-3583)

Malicious players can send null or invalid data to the built in plugin channels at the moment, causing a stack trace to be output.  This by itself isn't an issue, but it can be done repeatedly, hundreds of times a second.  This causes an immense amount of console spam and can lag/crash many servers by bottlenecking I/O or CPU.  It is easily fixed by commenting out the appropriate lines.

See: https://bukkit.atlassian.net/browse/BUKKIT-3583 for more information.