Add support for reassembling GOG Galaxy file parts

[hexpunk]

When I try to extract the files from GOG's "Unreal 2 - The Awakening Special Edition" installer, there are no errors or anything like that. However, the app directory is mostly empty. There's a commonappdata folder that I don't recall having seen with any of the other GOG installers. And most of the data is in the tmp directory, but broken up into very small pieces that appear to be parts of larger files that are addressed by hashes.

Here's a link to my output from just listing the contents of the installer. I would include it here, but it's too long for the body of a GitHub issue.

It's very bizarre and completely unusable. Any ideas as to what may be going on here?

[vv221]

This is a known issue due to a change in the way GOG packages their Windows games, you can read more about it on the GOG forums:

https://www.gog.com/forum/general/adamhms_linux_wine_wrappers_news_faq_discussion/post143

An innoextract fork allow to extract these installers:

https://github.com/immi101/innoextract/tree/gogextract

[hexpunk]

Good to know. Thank you.

[dscharrer]

Support for GOG Galaxy files has been added to innoextract 1.7 (to be released soon), a release candidate is available for testing.

Current limitations:

• Architecture and OS constraints are ignored (language constraints are supported and there is a warning for non-default architecture and OS constraints) - are these used anywhere?
• All parts of the same file must have the same constraints (there is a warning for this also the first part contains a checksum for the whole file so this is likely OK)

Current advantages over gogextract:

• GOG Galaxy files are handled without the --gog option for installers published by GOG.com (the --gog option still forces it for all installers)
• Dependencies (ie before_install_dependency/after_install_dependency) are also extracted
• Collisions (overwriting/renaming) works correctly for multi-part files
• GOG Galaxy language constraints are handled via the --languageand --language-only options just like normal Inno Setup language constraints
• --list-languages lists languages used in GOG Galaxy constraints
• The re-assembled file is validated against the file checksum
• The output file is opened only once for multi-part files