jpx_codestream_source::get_stream_loc

The returned jp2_locator object may be used to open the contiguous codestream box, or fragment table box which is associated with the actual code-stream data. This function will never return a null locator (i.e., jp2_locator::is_null will never return true), even where a JPX file is dynamically served via JPIP. The reason is that jpx_source::access_codestream will return a non-empty jpx_codestream_source interface only once sufficient information has become available for the codestream itself at least to be opened.