tdf#136577 sw: fix Undo of Replace with nothing

The UI doesn't allow to replace an empty selection anyway, but it now
happens on Undo.

(regression from e1629c210ad78310e3d48c0756723134a27b89df)

Change-Id: I468f28335beaeb8c42df8ed4cfc90f2c03129239
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/104308
Tested-by: Jenkins
Reviewed-by: Michael Stahl <michael.stahl@cib.de>
(cherry picked from commit d3eca4177a78c3db17b4699ea6e071e52488c46f)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/104305
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
diff --git a/sw/source/core/doc/DocumentContentOperationsManager.cxx b/sw/source/core/doc/DocumentContentOperationsManager.cxx
index bee95be..17bbd2b 100644
--- a/sw/source/core/doc/DocumentContentOperationsManager.cxx
+++ b/sw/source/core/doc/DocumentContentOperationsManager.cxx
@@ -4256,7 +4256,7 @@ bool DocumentContentOperationsManager::DeleteRangeImplImpl(SwPaM & rPam)
bool DocumentContentOperationsManager::ReplaceRangeImpl( SwPaM& rPam, const OUString& rStr,
        const bool bRegExReplace )
{
    if( !rPam.HasMark() || *rPam.GetPoint() == *rPam.GetMark() )
    if (!rPam.HasMark())
        return false;

    bool bJoinText, bJoinPrev;