input: remove redundant test
input: remove redundant test

If demux_t.s is NULL, then the b_rescale_ts flag is true and the
DEMUX_SET_RATE control will fail. The end result is the same.

xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc