backends/winrt: check watcher status after starting

If Bluetooth is off or not present, the status will be ABORTED. We can
use this to give a helpful error message.

Also wait some time for the status to change to STARTED before returning.

Fixes: #1535

CHANGELOG.rst

@@ -27,6 +27,7 @@ Fixed
 * Fixed ``KeyError`` in BlueZ ``is_connected()`` and ``get_global_bluez_manager()`` when device is not present. Fixes #1507.
 * Fixed BlueZ ``_wait_removed`` completion on invalid object path. Fixes #1489.
 * Fixed rare unhandled exception when scanning on macOS when using ``use_bdaddr``. Fixes #1523.
+* Fixed scanning silently failing on Windows when Bluetooth is off. Fixes #1535.
 
 `0.21.1`_ (2023-09-08)
 ======================

bleak/backends/winrt/scanner.py

@@ -248,6 +248,16 @@ async def start(self) -> None:
 
         self.watcher.start()
 
+        # no events for status changes, so we have to poll :-(
+        while self.watcher.status == BluetoothLEAdvertisementWatcherStatus.CREATED:
+            await asyncio.sleep(0.01)
+
+        if self.watcher.status == BluetoothLEAdvertisementWatcherStatus.ABORTED:
+            raise BleakError("Failed to start scanner. Is Bluetooth turned on?")
+
+        if self.watcher.status != BluetoothLEAdvertisementWatcherStatus.STARTED:
+            raise BleakError(f"Unexpected watcher status: {self.watcher.status.name}")
+
     async def stop(self) -> None:
         self.watcher.stop()