avformat: introduce AVFormatContext io_close2 which returns an int

Otherwise there is no way to detect an error returned by avio_close() because ff_format_io_close cannot get the return value. Checking the return value of the close function is important in order to check if all data was successfully written and the underlying close() operation was successful. It can also be useful even for read mode because it can return any pending AVIOContext error, so the user don't have to manually check AVIOContext->error. In order to still support if the user overrides io_close, the generic code only uses io_close2 if io_close is either NULL or the default io_close callback.

MBMarton Balint committed 4 years ago