gltrace: Return sensible value for GL_MAX_DEBUG_MESSAGE_LENGTH when faking KHR_debug.
gltrace: Return sensible value for GL_MAX_DEBUG_MESSAGE_LENGTH when faking KHR_debug.

`apitrace trace glretrace ...` relies on it.

trtt/apitrace,schulmar/apitrace,apitrace/apitrace,apitrace/apitrace,trtt/apitrace,schulmar/apitrace,apitrace/apitrace,schulmar/apitrace,schulmar/apitrace,apitrace/apitrace,trtt/apitrace,schulmar/apitrace,trtt/apitrace,trtt/apitrace