ildaeil: fix ImGui assertion error in debug builds

[Simon-L]

Empty widgets labels generate IDs that conflict with the main window.

This fixes the assertion error with ImGui in debug builds:

Cardinal/src/DearImGui/imgui_widgets.cpp:632: bool ImGui::ButtonBehavior(const ImRect&, ImGuiID, bool*, bool*, ImGuiButtonFlags): Assertion mouse_button >= 0 && mouse_button < ImGuiMouseButton_COUNT' failed.

See ocornut/imgui#4796 which is precisely the same issue.
More info: https://github.com/ocornut/imgui/blob/master/docs/FAQ.md#q-how-can-i-have-widgets-with-an-empty-label

[falkTX]

Thanks!