sw_redlinehide: fix SwGetExpField ODF import

After import, SwGetExpField are empty if ShowRedlineChanges=false
because the content from the document is lost in SwGetExpField::Copy().

Example is ooo26330-3.sxw, which then asserts once fields are updated,
but that is a different problem.

(regression from 57f358f1ac4f3e05fcdf54326388ba8a19f0f2b3)

Change-Id: I1bf939d69e599919c3a5c5631091ca0a0074d139
Reviewed-on: https://gerrit.libreoffice.org/68820
Tested-by: Jenkins
Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>

sw/source/core/fields/expfld.cxx

@@ -331,6 +331,7 @@ std::unique_ptr<SwField> SwGetExpField::Copy() const
     pTmp->m_fValueRLHidden = m_fValueRLHidden;
     pTmp->SwValueField::SetValue(GetValue());
     pTmp->m_sExpand       = m_sExpand;
+    pTmp->m_sExpandRLHidden = m_sExpandRLHidden;
     pTmp->m_bIsInBodyText  = m_bIsInBodyText;
     pTmp->SetAutomaticLanguage(IsAutomaticLanguage());
     if( m_bLateInitialization )