tdf#121275 fallback to gtk3 under wayland with unknown desktop

Change-Id: Ie63da823faf9067e61ca4870f464d49425bbc907
Reviewed-on: https://gerrit.libreoffice.org/63123
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>
diff --git a/vcl/unx/generic/desktopdetect/desktopdetector.cxx b/vcl/unx/generic/desktopdetect/desktopdetector.cxx
index b446f7c3..e7cb9b9 100644
--- a/vcl/unx/generic/desktopdetect/desktopdetector.cxx
+++ b/vcl/unx/generic/desktopdetect/desktopdetector.cxx
@@ -280,6 +280,12 @@
        ret = DESKTOP_LXQT;
    else
    {
        // tdf#121275 if we still can't tell, and WAYLAND_DISPLAY
        // is set, default to gtk3
        const char* pWaylandStr = getenv("WAYLAND_DISPLAY");
        if (pWaylandStr && *pWaylandStr)
            return DESKTOP_GNOME;

        // these guys can be slower, with X property fetches,
        // round-trips etc. and so are done later.