Fix uninitialized variable errors in release mode

When using `meson --buildtype=release`, `-Wextra -Werror` is passed.
This includes `-Werror=maybe-uninitialized`, which complains about
the instances fixed in this commit.

backend/wayland/seat.c

@@ -468,7 +468,7 @@ struct wlr_wl_input_device *create_wl_input_device(
 
 	unsigned int vendor = 0, product = 0;
 
-	const char *type_name;
+	const char *type_name = "unknown";
 
 	switch (type) {
 	case WLR_INPUT_DEVICE_KEYBOARD:

tinywl/tinywl.c

@@ -475,7 +475,7 @@ static void server_cursor_button(struct wl_listener *listener, void *data) {
 	wlr_seat_pointer_notify_button(server->seat,
 			event->time_msec, event->button, event->state);
 	double sx, sy;
-	struct wlr_surface *surface;
+	struct wlr_surface *surface = NULL;
 	struct tinywl_view *view = desktop_view_at(server,
 			server->cursor->x, server->cursor->y, &surface, &sx, &sy);
 	if (event->state == WLR_BUTTON_RELEASED) {