Make multibuffer anchor's buffer_id optional

Avoid using 0 for a buffer id on Anchor::min and max

Co-Authored-By: Antonio Scandurra <me@as-cii.com>
Co-Authored-By: Nathan Sobo <nathan@zed.dev>
947fe848c1Max Brunsfeld committed on 2/11/2022, 5:51:47 PMparentfa194c8
3 files changedLine totals unavailable