fix useless assign

typo from commit a5991960
Date:   Mon Sep 30 14:38:41 2013 +0200
    covnert sc/source/filter/inc/namebuff.hxx from String to OUString

'=' should have been '+='
was 'aScAbsName.AppendAscii( RTL_CONSTASCII_STRINGPARAM( "_ABS" ) );'

Change-Id: Ic9c6dcd5c7871c35ae44e6be0f8314d073a863b3
Reviewed-on: https://gerrit.libreoffice.org/33556Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

sc/source/filter/inc/namebuff.hxx

@@ -87,12 +87,11 @@ private:
                             Entry( const OUString& rName, const OUString& rScName, const ScComplexRefData& rCRD )
                                 : aStrHashEntry( rName )
                                 , aScComplexRefDataRel( rCRD )
-                                , aScAbsName( rScName )
+                                , aScAbsName( rScName + "_ABS" )
                                 , nAbsInd(0)
                                 , nRelInd(0)
                                 , bSingleRef(false)
                             {
-                                aScAbsName = "_ABS";
                             }
     };