call receiveNumber in onDataReceived to flush queue if needed (startup race)

fixed simulator issue when event onDataReceived gets raised

sim/libmbit.ts

@@ -517,6 +517,7 @@ namespace pxsim.radio {
 
     export function onDataReceived(handler: RefAction): void {
         pxt.registerWithDal(DAL.MICROBIT_ID_RADIO, DAL.MICROBIT_RADIO_EVT_DATAGRAM, handler);
+        radio.receiveNumber();
     }
 }
 

sim/state.ts

@@ -72,10 +72,9 @@ namespace pxsim {
         }
 
         queue(packet: PacketBuffer) {
-            if (this.datagram.length < 5) {
+            if (this.datagram.length < 4)
                 this.datagram.push(packet);
-                (<Board>runtime.board).bus.queue(DAL.MICROBIT_ID_RADIO, DAL.MICROBIT_RADIO_EVT_DATAGRAM);
-            }
+            (<Board>runtime.board).bus.queue(DAL.MICROBIT_ID_RADIO, DAL.MICROBIT_RADIO_EVT_DATAGRAM);
         }
 
         send(buffer: number[] | string) {