tdf#121686: fix assert in SvxAutoCorrect::FnChgToEnEmDash (editeng)

See https://bugs.documentfoundation.org/attachment.cgi?id=149773

Change-Id: I1696984a8df1b38a359a8177a5f3670526d2696e
Reviewed-on: https://gerrit.libreoffice.org/68832
Tested-by: Jenkins
Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>
(cherry picked from commit 67d170868401335434772f1be23d565d23c1fbea)
Reviewed-on: https://gerrit.libreoffice.org/68882
diff --git a/editeng/source/misc/svxacorr.cxx b/editeng/source/misc/svxacorr.cxx
index b890b5c..737225d 100644
--- a/editeng/source/misc/svxacorr.cxx
+++ b/editeng/source/misc/svxacorr.cxx
@@ -542,7 +542,8 @@ bool SvxAutoCorrect::FnChgToEnEmDash(
        sal_Unicode cCh = rTxt[ nSttPos ];
        if( '-' == cCh )
        {
            if( ' ' == rTxt[ nSttPos-1 ] &&
            if( 1 < nEndPos - nSttPos &&
                ' ' == rTxt[ nSttPos-1 ] &&
                '-' == rTxt[ nSttPos+1 ])
            {
                sal_Int32 n;