lokdocview: Set a 'default' path for LOK init

When passed NULL to lok_doc_view_new, use the default path :
$libdir/libreoffice/program as LOK install path

Change-Id: I1e033c407184b29b1509cfb8c416b514591d67ce
Reviewed-on: https://gerrit.libreoffice.org/20476Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: David Tardon <dtardon@redhat.com>
(cherry picked from commit 424c09b1)

include/LibreOfficeKit/LibreOfficeKitGtk.h

@@ -42,7 +42,8 @@ GType                          lok_doc_view_get_type               (void) G_GNUC
 
 /**
  * lok_doc_view_new:
- * @pPath: LibreOffice install path.
+ * @pPath: (nullable): LibreOffice install path. Pass null to set it to default
+ * path which in most cases would be $libdir/libreoffice/program
  * @cancellable: The cancellable object that you can use to cancel this
  * operation.
  * @error: The error that will be set if the object fails to initialize.

libreofficekit/Library_libreofficekitgtk.mk

@@ -28,6 +28,10 @@ $(eval $(call gb_Library_add_libs,libreofficekitgtk,\
     $(GTK3_LIBS) \
 ))
 
+$(eval $(call gb_Library_add_defs,libreofficekitgtk,\
+	-DLOK_PATH="\"$(LIBDIR)/libreoffice/$(LIBO_LIB_FOLDER)\"" \
+))
+
 ifeq ($(OS),$(filter LINUX %BSD SOLARIS, $(OS)))
 $(eval $(call gb_Library_add_libs,libreofficekitgtk,\
     $(DLOPEN_LIBS) -lm \

libreofficekit/source/gtk/lokdocview.cxx

@@ -2387,7 +2387,7 @@ static void lok_doc_view_class_init (LOKDocViewClass* pClass)
 SAL_DLLPUBLIC_EXPORT GtkWidget*
 lok_doc_view_new (const gchar* pPath, GCancellable *cancellable, GError **error)
 {
-    return GTK_WIDGET (g_initable_new (LOK_TYPE_DOC_VIEW, cancellable, error, "lopath", pPath, NULL));
+    return GTK_WIDGET (g_initable_new (LOK_TYPE_DOC_VIEW, cancellable, error, "lopath", pPath == NULL ? LOK_PATH : pPath, NULL));
 }
 
 SAL_DLLPUBLIC_EXPORT GtkWidget* lok_doc_view_new_from_widget(LOKDocView* pOldLOKDocView)