shell: Do not insert input panel layer when locked

Do not try to insert the input panel layer in the layer list when the
shell is locked in show_input_panels(). The layer will already be
insrted in resume_desktop() anyways.

https://bugs.freedesktop.org/show_bug.cgi?id=56543

Signed-off-by: Jan Arne Petersen <jpetersen@openismus.com>

src/shell.c

@@ -2780,6 +2780,7 @@ show_input_panels(struct wl_listener *listener, void *data)
 
 	shell->showing_input_panels = true;
 
+	if (!shell->locked)
 		wl_list_insert(&shell->panel_layer.link,
 			       &shell->input_panel_layer.link);