Fix the read implementation on no-std

[AldaronLau]

Currently behavior is panicking.

[Robbepop]

LGTM

Thanks a lot for the bug fix!
How did you encounter this bug?

[AldaronLau]

@Robbepop I found the bug by trying to convert the example in lib.rs to work on no-std, as I was upgrading one of my projects from an older version of wasmi. First, I had to get rid of the &mut from the call to Module::new() - then it compiled. After that, I tried loading my WASM file, and I got an unexpected panic.

[Robbepop]

@AldaronLau btw the new wasmi engine is still pretty new and therefore not yet battle hardened. We are currently in the process to change that. As of right now I would not recommend using the newest wasmi in production. We are thankful for using wasmi in non-production use cases to battle harden it thought. :)

[AldaronLau]

@Robbepop thanks for the warning. I don't think my project counts a "production" (it's very experimental), so I'll keep testing it.

[Robbepop]

@AldaronLau Do you have a link to the experimental project for me?

[AldaronLau]

The project is https://github.com/ardaku/quantii, which pulls in https://github.com/ardaku/ardaku, which I was updating to the new version of wasmi.