ffmpeg: dont call read_key() in decode_interrupt_cb() this can cause keys to be lost

also its slow when read_key() is slow and there are a very large number of calls
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg.c

@@ -614,7 +614,6 @@ static int read_key(void)
 
 static int decode_interrupt_cb(void)
 {
-    q_pressed += read_key() == 'q';
     return q_pressed > 1;
 }