channel-display-gst: Protect timer_id with queue_mutex
channel-display-gst: Protect timer_id with queue_mutex

timer_id is supposed to be protected by this mutex, make sure this
is true in spice_gst_decoder_reschedule.

Signed-off-by: Frediano Ziglio <55d48b080b2e443e395cde84d2c83b135a4ff48e@redhat.com>
Acked-by: Snir Sheriber <a22152bc672d3e177f23883338efc60c231ec881@redhat.com>

flexVDI/spice-gtk,flexVDI/spice-gtk