OpenRead function in as_02_IAB.cpp should be const

[kblinova]

as-02-info FileInfoWrapper would need a special method when it is modified to support IAB essence because it relies on OpenRead functions to be const.

The const'ness of OpenRead method is achieved by delegating the implementation of the reading to an internal class (see h__Reader in other implementations).

[palemieux]

The const'ness of OpenRead method is achieved by delegating the implementation of the reading to an internal class (see h__Reader in other implementations).

I do not know how this is possible. For example, AS_02::JP2K::MXFReader::OpenRead() is defined as const but in fact modifies its internal state through a non-const method call on its own member: m_Reader->OpenRead(filename).

[jhursty]

The established pattern in the library is that reader instances will work properly when declared const. Whether or not one may agree with it the pattern nonetheless is established and should not be ignored.

[palemieux]

@jhursty What is the objective of defining OpenRead() as const?