Don't dispose a serial session if it's not open

Respect the number of serial listeners and only start and stop
serial when required.

Author: microbit-robert

lib/usb-radio-bridge.ts

@@ -83,7 +83,10 @@ class MicrobitRadioBridgeConnectionImpl
     const currentStatus = this.status;
     if (e.status !== ConnectionStatus.CONNECTED) {
       this.setStatus(e.status);
-      this.serialSession?.dispose();
+      if (this.serialSessionOpen) {
+        // If the session is already closed we don't need to dispose.
+        this.serialSession?.dispose();
+      }
     } else {
       this.status = ConnectionStatus.DISCONNECTED;
       if (

lib/usb.ts

@@ -564,6 +564,10 @@ class MicrobitWebUSBConnectionImpl
   protected eventActivated(type: string): void {
     switch (type as keyof SerialConnectionEventMap) {
       case "serialdata": {
+        if (this.addedListeners.serialdata) {
+          this.addedListeners.serialdata++;
+          break;
+        }
         // Prevent starting serial when flashing.
         if (!this.flashing) {
           this.startSerialInternal();
@@ -578,8 +582,10 @@ class MicrobitWebUSBConnectionImpl
   protected async eventDeactivated(type: string) {
     switch (type as keyof SerialConnectionEventMap) {
       case "serialdata": {
-        this.stopSerialInternal();
         this.addedListeners.serialdata--;
+        if (!this.addedListeners.serialdata) {
+          this.stopSerialInternal();
+        }
         break;
       }
     }