dpms/wayland: Explicitly set as unsupported if addRegistryListener didn't find the interface
If a org_kde_kwin_dpms_manager wasn't found, setSupported(false) so that the user gets closure. BUG: 466181
If a org_kde_kwin_dpms_manager wasn't found, setSupported(false) so that the user gets closure. BUG: 466181
mentioned in commit 1515b653