demux: ts: fix divbyzero

modules/demux/mpeg/ts.c

@@ -1531,9 +1531,12 @@ static int Control( demux_t *p_demux, int i_query, va_list args )
             i_length += p_pmt->pcr.i_pcroffset;
             double i_pos = TimeStampWrapAround( p_pmt,
                                                 p_pmt->pcr.i_current ) - p_pmt->pcr.i_first;
+            if( i_length > 0 )
+            {
                 *pf = i_pos / i_length;
                 return VLC_SUCCESS;
             }
+        }
 
         if( (i64 = stream_Size( p_sys->stream) ) > 0 )
         {