Fix HUD text display taking over other plugins' display

[zer0k-z]

Related to #419, but does not really fix it because MHUD is still at fault.

The reuse logic with 6 channels is fine, and is not why the HUD text was unable to be displayed.
The cause is the client's internal message buffer which is 16 slots long and shared between 6 channels at once. The message in the buffer will only clear once the hold time is over. So a plugin sending one HUD message lasting for 0.5 seconds will immediately fill the buffer (that's 64 messages, which is way past 16), leaving no place for other plugins.

The reason joining team or sending round_start event temporarily fixes the issue is because they trigger the message buffer wipe, but they come with other unwanted side effects.

Reference

[zer0k-z]

This should also fix speed text anti aliasing being broken.