pbio/drv/bluetooth: Fix peripheral disconnect if config unset.

The pbdrv_bluetooth_is_connected check should protect against this, but if it fails we get a segfault if config was never set, so if no peripheral was ever connected.

Author: laurensvalk

lib/pbio/drv/bluetooth/bluetooth.c

@@ -188,8 +188,12 @@ pbio_error_t pbdrv_bluetooth_peripheral_disconnect(void) {
         return PBIO_SUCCESS;
     }
 
+    // Clear notification handler to avoid receiving further data.
+    if (peri->config) {
+        peri->config->notification_handler = NULL;
+    }
+
     // Initialize operation for handling on the main thread.
-    peri->config->notification_handler = NULL;
     peri->func = pbdrv_bluetooth_peripheral_disconnect_func;
     peri->err = PBIO_ERROR_AGAIN;
     pbio_os_request_poll();