fix error handling on openbsd too

Author: lovasoa

src/guess_os_stack_limit/openbsd.rs

@@ -1,8 +1,8 @@
 pub unsafe fn guess_os_stack_limit() -> Option<usize> {
     let mut stackinfo = std::mem::MaybeUninit::<libc::stack_t>::uninit();
-    assert_eq!(
-        libc::pthread_stackseg_np(libc::pthread_self(), stackinfo.as_mut_ptr()),
-        0
-    );
+    let res = libc::pthread_stackseg_np(libc::pthread_self(), stackinfo.as_mut_ptr());
+    if res != 0 {
+        return None;
+    }
     Some(stackinfo.assume_init().ss_sp as usize - stackinfo.assume_init().ss_size)
 }