gdal/cad_fuzzer: in CADHandle::getAsLong

Detailed report: https://oss-fuzz.com/testcase?key=6093626703609856 Project: gdal Fuzzer: aflgdalcadfuzzer Fuzz target binary: cadfuzzer Job Type: aflasangdal Platform Id: linux Crash Type: READ 8 Crash Address: 0x6020000428dd Crash State: CADHandle::getAsLong DWGFileRNUMBER::GetNOD...