worker: remove useless test
worker: remove useless test

red_channel_max_pipe_size returns 0 if no client (channel disconnected)
no need to check if cursor_channel/display_channel are NULL or
connected.

Signed-off-by: Frediano Ziglio <55d48b080b2e443e395cde84d2c83b135a4ff48e@redhat.com>
Acked-by: Jonathon Jongsma <jjongsma at redhat.com>

SPICE/spice,fgouget/spice,fgouget/spice,SPICE/spice,fgouget/spice,fgouget/spice,SPICE/spice