Dialog: Avoid using plasmashell protocol when running in kwin
KWindowSystem::isPlatformWayland() returns true if Dialog is created in kwin. However, in that case, it's highly undesired to try to use the plasma shell protocol.
KWindowSystem::isPlatformWayland() returns true if Dialog is created in kwin. However, in that case, it's highly undesired to try to use the plasma shell protocol.