zeroize: `tests::zeroize_c_string` fails on i386

Hi,

while testing zeroize on Debian infrastructure one test fails (it does not fail on other architectures).

---- tests::zeroize_c_string stdout ----
thread 'tests::zeroize_c_string' panicked at 'assertion failed: `(left == right)`
  left: `21`,
 right: `0`', src/lib.rs:936:17
stack backtrace:
   0: rust_begin_unwind
             at /usr/src/rustc-1.58.1/library/std/src/panicking.rs:498:5
   1: core::panicking::panic_fmt
             at /usr/src/rustc-1.58.1/library/core/src/panicking.rs:107:14
   2: core::panicking::assert_failed_inner
   3: core::panicking::assert_failed
             at /usr/src/rustc-1.58.1/library/core/src/panicking.rs:145:5
   4: zeroize::tests::zeroize_c_string
             at ./src/lib.rs:936:17
   5: zeroize::tests::zeroize_c_string::{{closure}}
             at ./src/lib.rs:922:5
   6: core::ops::function::FnOnce::call_once
             at /usr/src/rustc-1.58.1/library/core/src/ops/function.rs:227:5
   7: core::ops::function::FnOnce::call_once
             at /usr/src/rustc-1.58.1/library/core/src/ops/function.rs:227:5

Please find the full log at https://ci.debian.net/data/autopkgtest/testing/i386/r/rust-zeroize/22485575/log.gz

Any hints how to debug this?

Start at tests::zeroize_c_string in src/lib.rs around lines 922-936 and compare the Debian i386 failure with runs on other architectures. Use the linked Debian log to identify why the assertion sees 21 instead of 0; done means the test passes on i386 without regressing other architectures.