fix assert on load of fdo82018-3.docx

apparently arises when lacking font to display it

Change-Id: I934e43668f2f4d9c4e96736c004dfb0c250ef191

sw/source/core/text/guess.cxx

@@ -318,6 +318,10 @@ bool SwTxtGuess::Guess( const SwTxtPortion& rPor, SwTxtFormatInfo &rInf,
                                               rInf.GetIdx() - nFieldDiff - 1:
                                               0;
 
+            if ( nLangIndex > nDoNotStepOver &&
+                    rInf.GetTxt().getLength() == nLangIndex )
+                --nLangIndex;
+
             while ( nLangIndex > nDoNotStepOver &&
                     ! rCC.isLetterNumeric( rInf.GetTxt(), nLangIndex ) )
                 --nLangIndex;