sfx2: add missing header guard

Change-Id: Ide261670be475f5d54d9d12c701ad82470396aeb
(cherry picked from commit d990a876)

include/sfx2/lokhelper.hxx

@@ -7,6 +7,9 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
+#ifndef INCLUDED_SFX2_LOKHELPER_HXX
+#define INCLUDED_SFX2_LOKHELPER_HXX
+
 #include <sfx2/dllapi.h>
 
 class SfxViewShell;
@@ -23,4 +26,6 @@ public:
     static int getViews();
 };
 
+#endif
+
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */