JITServer: Pre-authentication remote crash via integer underflow and out-of-bounds heap read in DataDescriptor deserialization

In Eclipse OpenJ9 versions prior to 0.63.0, the JITServer component fails to perform cross-field validation on attacker-controlled `_size`, `_paddingSize`, and `_dataOffset` fields during `DataDescriptor` message deserialization. An unauthenticated remote attacker can send a crafted network payload that triggers an unsigned integer underflow in `DataDescriptor::getPayloadSize()` and `DataDescriptor::getNextDescriptor()`. This results in an out-of-bounds heap read and an immediate process crash (SIGSEGV), causing a denial of service.