Do not send overlay geometry to text input.

Observed in kirigami that it's VK space evading code will also use the overlay mode input method surface. This is because that Qt will always text-input set_input_panel_state size as QInputMethod.keyboardRectangle. Since Qt is the only text-input-v2 user, and I don't think it make much sense for application to do anything with overlay surface, just change it to send the empty rect if the mode is overlay.