tdf#97301: Return silently when no document is loaded

Change-Id: Id6cf77ee7597fb992a306649c2f2a3639bf6dad8
diff --git a/libreofficekit/source/gtk/lokdocview.cxx b/libreofficekit/source/gtk/lokdocview.cxx
index c7dceaa..742946d 100644
--- a/libreofficekit/source/gtk/lokdocview.cxx
+++ b/libreofficekit/source/gtk/lokdocview.cxx
@@ -2663,6 +2663,9 @@ lok_doc_view_set_zoom (LOKDocView* pDocView, float fZoom)
    LOKDocViewPrivate& priv = getPrivate(pDocView);
    GError* error = nullptr;

    if (!priv->m_pDocument)
        return;

    // Clamp the input value in [MIN_ZOOM, MAX_ZOOM]
    fZoom = fZoom < MIN_ZOOM ? MIN_ZOOM : fZoom;
    fZoom = fZoom > MAX_ZOOM ? MAX_ZOOM : fZoom;