Fix the rust allocator when std is not used

[bjorn3]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Files with missing lines	Coverage Δ
libbz2-rs-sys/src/allocator.rs	62.35% <100.00%> (ø)

[folkertdev]

is there a convenient way to test that rust-allocator can be used without std?

[bjorn3]

I used cargo build -p libbz2-rs-sys --no-default-features --features rust-allocator locally. I can add a CI check for that.

[folkertdev]

yes I think that's a good idea