fix for unused return value.

This code was introduced by:
   commit d09dd898
   Author: Frank Schoenheit [fs] <frank.schoenheit@sun.com>
   Date:   Wed Sep 15 13:55:34 2010 +0200
   dba34a: export/import min-/max-/default-/value for date/time as
   XML-Schema conformant strings
It looks like it intended to use determineDefaultServiceName(), but
neglected to store the return value.

Change-Id: I1607f39cf771b594389492785c7e72478d44843a
Reviewed-on: https://gerrit.libreoffice.org/4140Reviewed-by: Luboš Luňák <l.lunak@suse.cz>
Tested-by: Luboš Luňák <l.lunak@suse.cz>

xmloff/source/forms/elementimport.cxx

@@ -184,7 +184,7 @@ namespace xmloff
         }
 
         if ( m_sServiceName.isEmpty() )
-            determineDefaultServiceName();
+            m_sServiceName = determineDefaultServiceName();
 
         // create the object *now*. This allows setting properties in the various handleAttribute methods.
         // (Though currently not all code is migrated to this pattern, most attributes are still handled