Fuzzer caught another large malloc. This is caused by lack of boundary check
in Ap4OdheAtom causing underflow.

Earlier boundary checks were insufficient to prevent certain potential
payloads. This adds more boundary checks to prevent underflow of remains. I have
also remove the usage of GetHeaderSize in constructor as it is a virtual method.

Fuzzer caught another large malloc. This is caused by lack of boundary check
in Ap4SbgpAtom causing underflow.

Fuzzer caught another large malloc in Ap4SbgpAtom. It is caused by overflow
in boundary check

The lack of boundary checks in Ap4ContainerAtom leads to an underflow
in size which then leads to existing validation checks to fail and hence allow
large malloc.

Same problem as before, underflow of bytes_available results in some potential
attack