emit, MQTT module and event name too long

Ok, just got it working with longer constants.

I think the issue was (and it's a bit of a hack), jsvGetString fills the buffer up and terminates with a 0, and returns the amount of characters written in that buffer. However in order for it to be 'safe' when people just use it without checking, even if there are more characters than allowed it can still only return the size of the buffer - so you're effectively wasting one character at the end - if that gets used you just assume it overflowed, even if it might have 'just fitted'.