[TODO] [Improve Security] Remove assert

[Syoyo Fujita]

Describe the issue

Remove assert and return error with proper error message for better security and code quality.

To Reproduce

N/A

Expected behavior

No assertion(and abort) in the code

Environment

N/A

[Syoyo Fujita]

Now tinyexr is assert free!

48870fb

TODO: Remove assert in miniz(or use wuff's zlib https://github.com/google/wuffs)