Unify way to check readable blender files.

[feuerste]

Previously the InternReadFile logic was much more restrictive than the CanRead logic, but able to also parse compressed files. With this change the behavior is unified.

[turol]

You should not pass shared_ptr via reference. Either pass by value or pass the raw pointer.

[feuerste]

I agree that we usually shouldn't pass smart pointers by reference.
However, in this specific case the stream is an input/output parameter, as it can internally be reset, if the file is compressed, and will be reused outside of this function. So passing by value wouldn't work. Passing by raw pointer would require us to clean up the old memory, so the whole point of using smart pointers is lost.

Of course if you wished we could rewrite more of the code here, but I didn't want to touch too much of the original logic (besides converting exceptions to strings).

[feuerste]

@turol Would you mind to restart the workflows and take another look? Thanks a lot!

[turol]

I still don't like the use of reference parameters. I think the correct solution would be to return a std::variant with either an error or the new buffer/stream. This might require C++ 17 however.

[kimkulling]

Looks fine!

[feuerste]

I still don't like the use of reference parameters. I think the correct solution would be to return a std::variant with either an error or the new buffer/stream. This might require C++ 17 however.

@turol I removed all reference arguments and created a helper struct to contain the stream, optional uncompressed data, and error. This is under the assumption that we still want to compile with < c++17 and have no variant support.
I think it is much cleaner now. PTAL!

[turol]

If you're going to rebase it you might as well squash the whole thing into one commit.

[feuerste]

If you're going to rebase it you might as well squash the whole thing into one commit.

Done.

[kimkulling]

Merged, thanks a lot for your contribution.