implement the 'freeze' function for incoming frames;

fix a bug which caused a crash when a videodevice was
specified after startgui=1 in the config file. This also
involves a slightly different method to determine if the
gui is active or not.



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@126572 65c4cc65-6c06-0410-ace0-fbb531ad65f3