zsh:funcs:nvim-man: Use man if option is passed

If an option without arguments like `--version` is passed, `nvim-man`
should use `command man` as well.

.config/zsh/zshrc.d/40-functions.zsh

@@ -397,7 +397,9 @@ git-commit-last-msg() {
 }
 
 nvim-man() {
-	if (( $+commands[nvim] && $# == 1 )); then
+	# Use nvim only if it exists, there was just one argument passed and that
+	# argument is not an option (e.g. `--version`)
+	if (( $+commands[nvim] && $# == 1 && $1 == ${1#-} )); then
 		# Check for existence of man page.
 		command man -w "$1" >/dev/null || return