Connector/C++: heap out-of-bounds read when malicious server field length exceeds declared column length in binary result path

MariaDB Connector/C++ sizes each result-column bind buffer to the column length the server declared at PREPARE time, but then reads `bind.length_value` - the actual field length the server reports in each row packet - bytes out of that buffer. libmariadb sets `length_value` to the full server-sent …

length      = columnInfo->getLength();     // server-declared column length
bind.back().buffer_length =
    columnInfo->getColumnType().binarySize() != 0 ?
    columnInfo->getColumnType().binarySize() :
    getLengthMaxFieldSize();               // == declared column length for string/blob types …