init: silence zcompdump metadata write for invalid ZSH_COMPDUMP filenames

If `$SHORT_HOST` contains invalid filename characters, the compinit call doesn't
error, but the zcompdump metadata write does. Use `tee` instead so we can silence
the error.

See https://github.com/ohmyzsh/ohmyzsh/commit/dd1a72696f162fd5285a104b5f63970deb66e8b0#commitcomment-38984764