address_space_stw_le_cached: Assertion `addr < cache->len && 2 <= cache ->len - addr' failed

When running OpenBSD-current as a guest, the following assertion is hit after a few seconds, resulting in the virtual machine to crash:

```
qemu-system-x86_64: /build/qemu/src/qemu-3.0.0/include/exec/memory_ldst_cached.inc.h:85: address_space_stw_le_cached: Assertion `addr < cache->len && 2 <= cache->len - addr' failed.
```

Host is Arch Linux stable, running on x86_64.

Qemu version is 3.0.0, installed via the standard Arch Linux package.

Version 2.12.1 didn't exhibit this behavior.