Don't exit transfer thread if an error occurs.

In the case of a libusb error, we still need the transfer thread
running, in order to handle outstanding cancellations and to signal the
condition variable when that is done.

host/libhackrf/src/hackrf.c

@@ -1766,7 +1766,7 @@ static void LIBUSB_CALL hackrf_libusb_transfer_callback(struct libusb_transfer*
 		LIBUSB_TRANSFER_ERROR, LIBUSB_TRANSFER_TIMED_OUT
 		LIBUSB_TRANSFER_STALL,	LIBUSB_TRANSFER_OVERFLOW ....
 		*/
-		request_exit(device); /* Fatal error stop transfer */
+		transfer_finished(device, usb_transfer);
 		device->streaming = false;
 	}
 }