4a7dab0f20
sys_write passes u64::MAX as offset for non-positioned file descriptors. ContextHandle::Start used an inline 'offset != 0' check which rejected u64::MAX, causing EINVAL when bootstrap called start_fd.write(&[0]) during fork_inner(). Replaced with require_zero_offset() which accepts both 0 and u64::MAX (fixed in the previous commit for the same class of bug).