red_worker: don't get bit_rate from main_channel_client, if it wasn't initialized
red_worker: don't get bit_rate from main_channel_client, if it wasn't initialized

When setting an initial video stream bit rate, if the bit rate
wasn't calculated by main_channel_client, and we don't have
estimation from previos streams, use some default values.
The patch also removes updating dcc->streams_max_bit_rate when
the bit_rate held by the main_channel is larger than it. It is not necessary
since we compare those 2 values each time we set the initial bit rate
for a stream.

freedesktop-unofficial-mirror/spice__spice,elmarco/spice,elmarco/spice,SPICE/spice,freedesktop-unofficial-mirror/spice__spice,alon/spice-server,ya-mouse/spice,alon/spice-server,freedesktop-unofficial-mirror/spice__spice,fgouget/spice,fgouget/spice,Fantu/spice,fgouget/spice,alon/spice-server,fgouget/spice,elmarco/spice,ya-mouse/spice,Fantu/spice,ya-mouse/spice,freedesktop-unofficial-mirror/spice__spice,SPICE/spice,Fantu/spice,freedesktop-unofficial-mirror/spice__spice,alon/spice-server,Fantu/spice,alon/spice-server,elmarco/spice,SPICE/spice,elmarco/spice