decoder: flush when prerolling too

This fixes a possible deadlock when seeking paused at the end of the video.
Indeed, in that case, prerolling won't end and the decoder won't be flushed if
we seek at the end again.

Conflicts:
    src/input/decoder.c
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

src/input/decoder.c

@@ -1366,14 +1366,6 @@ static void DecoderProcessFlush( decoder_t *p_dec )
     if( p_dec->b_error )
         return;
 
-    vlc_mutex_lock( &p_owner->lock );
-    if ( p_owner->i_preroll_end == INT64_MAX )
-    {
-        vlc_mutex_unlock( &p_owner->lock );
-        return;
-    }
-    vlc_mutex_unlock( &p_owner->lock );
-
     if( p_packetizer != NULL && p_packetizer->pf_flush != NULL )
         p_packetizer->pf_flush( p_packetizer );