tdf#76995: updated cached value on Evaluate() of db name field

Conversion of fields to text while creating mail merge documents
returns a cached value. This needs to be set before also for db name fields.

Change-Id: I5796adc82e11005ea045fb220b81201db5ff0b28
Reviewed-on: https://gerrit.libreoffice.org/19806Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Oliver Specht <oliver.specht@cib.de>

sw/source/core/doc/DocumentFieldsManager.cxx

@@ -988,6 +988,7 @@ void DocumentFieldsManager::UpdateExpFields( SwTextField* pUpdateField, bool bUp
         {
             const_cast<SwDBSetNumberField*>(static_cast<const SwDBSetNumberField*>(pField))->Evaluate(&m_rDoc);
             aCalc.VarChange( sDBNumNm, static_cast<const SwDBSetNumberField*>(pField)->GetSetNumber());
+            pField->ExpandField(m_rDoc.IsClipBoard());
         }
 #endif
         break;