Problem: running `nvim oil-ssh://host/` from the command line sometimes
emits "Oil split could not find parent window" immediately on startup.
The `WinNew` autocmd that transfers oil window vars to new splits fires
during startup before `BufEnter` has set `oil_did_enter` on any window,
so the parent search finds nothing and warns.
Solution: guard the callback with `vim.v.vim_did_enter ~= 1` so it is
silently skipped during the pre-`VimEnter` startup phase. After
`VimEnter` the split-transfer logic runs unchanged. `vim_did_enter` is
already used in `setup()` for the same startup-completion check.
Based on: stevearc/oil.nvim#325
Barrett Ruth
36c07875d2
