tdf#95687: Wrong function names in Formula Writer are considered as SUM

Just indicate there's an error if the function name is unknown

Change-Id: Idad6dd1911c2e8a0206f70fb933fcfd540a887d2
Reviewed-on: https://gerrit.libreoffice.org/19919Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>

sw/source/core/bastyp/calc.cxx

@@ -713,7 +713,7 @@ SwCalcOper SwCalc::GetToken()
             }
             aVarName = aName;
             eCurrOper = CALC_NAME;
-            bSetError = false;
+            bSetError = true;
         }
         else if ( aRes.TokenType & KParseType::DOUBLE_QUOTE_STRING )
         {