Send serial data to sim uart only if rx_ready is set.

litex/build/sim/core/modules/serial2console/serial2console.c

@@ -155,12 +155,14 @@ static int serial2console_tick(void *sess, uint64_t time_ps) {
   }
 
   *s->rx_valid = 0;
+  if(*s->rx_ready) {
     if(s->datalen) {
       *s->rx = s->databuf[s->data_start];
       s->data_start = (s->data_start + 1) % 2048;
       s->datalen--;
       *s->rx_valid = 1;
     }
+  }
 
   return RC_OK;
 }