nsv: Don't cast function return.

modules/demux/nsv.c

@@ -331,7 +331,8 @@ static int Control( demux_t *p_demux, int i_query, va_list args )
             i64 = stream_Size( p_demux->s );
             if( i64 > 0 )
             {
-                *pf = (double)stream_Tell( p_demux->s ) / (double)i64;
+                double current = stream_Tell( p_demux->s );
+                *pf = current / (double)i64;
             }
             else
             {