lib: force wait state after cancel of usb transfer

..and before handling usb events

This avoids an occasional crash when closing the device on Windows.
Also see https://github.com/libusb/libusb/issues/1043.

src/librtlsdr.c

@@ -1930,6 +1930,9 @@ int rtlsdr_read_async(rtlsdr_dev_t *dev, rtlsdr_read_async_cb_t cb, void *ctx,
 					/* handle events after canceling
 					 * to allow transfer status to
 					 * propagate */
+#ifdef _WIN32
+					Sleep(1);
+#endif
 					libusb_handle_events_timeout_completed(dev->ctx,
 									       &zerotv, NULL);
 					if (r < 0)