[h323plus] H323Plus bugs

Hi,

i fixed 2 possible crashes on Github. A few weeks ago there were also fixes for H.460.22 messages.

There is a pending bug that H323Plus is not handling assigned gatekeepers correctly. It always connects to the assigned gatekeeper even if its down instead of staying on the current gatekeeper until the assigned gatekeeper becomes available again. This will need a bigger fix.

Regards, Jan