minor tweak to existing fix for ( bnc#660816 & fdo#34908

it seems the orig commit ( af4d6062b7e676ed56dc84927fb99b79aa03a7b5 ) when tweaked for libreoffice3.3 had a little mistake introduced ( which then go ported into master )

sw/source/core/crsr/bookmrk.cxx

@@ -332,9 +332,9 @@ namespace sw { namespace mark
     }
     void CheckboxFieldmark::SetChecked(bool checked)
     {
-        (*GetParameters())[::rtl::OUString(RTL_CONSTASCII_USTRINGPARAM(ODF_FORMCHECKBOX_RESULT))] = makeAny(checked);
         if ( IsChecked() != checked )
         {
+            (*GetParameters())[::rtl::OUString(RTL_CONSTASCII_USTRINGPARAM(ODF_FORMCHECKBOX_RESULT))] = makeAny(checked);
             // mark document as modified
             SwDoc *const pDoc( GetMarkPos().GetDoc() );
             if ( pDoc )