tdf#120576 avoid crash during database migration

0xFFFF cast to short turned into -1 so wasn't seen as > 8000

Change-Id: I57592020c3c31751bec43f2619bf65d41ac47e87
Reviewed-on: https://gerrit.libreoffice.org/65538
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>
diff --git a/connectivity/source/drivers/firebird/PreparedStatement.cxx b/connectivity/source/drivers/firebird/PreparedStatement.cxx
index e0d120d..648f3f6 100644
--- a/connectivity/source/drivers/firebird/PreparedStatement.cxx
+++ b/connectivity/source/drivers/firebird/PreparedStatement.cxx
@@ -208,7 +208,7 @@ void SAL_CALL OPreparedStatement::setString(sal_Int32 nParameterIndex,
        {
            str = str.copy(0, max_varchar_len);
        }
        const short nLength = str.getLength();
        const auto nLength = str.getLength();
        memcpy(pVar->sqldata, &nLength, 2);
        // Actual data
        memcpy(pVar->sqldata + 2, str.getStr(), str.getLength());
@@ -847,7 +847,7 @@ void SAL_CALL OPreparedStatement::setBytes(sal_Int32 nParameterIndex,
            {
                xBytesCopy.realloc( nMaxSize );
            }
            const short nSize = xBytesCopy.getLength();
            const auto nSize = xBytesCopy.getLength();
            // 8000 corresponds to value from lcl_addDefaultParameters
            // in dbaccess/source/filter/hsqldb/createparser.cxx
            if (nSize > 8000)