skip atuin init when encryption key is missing or empty

Prevents panic on fresh installs where atuin has no key yet.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

private_dot_config/private_fish/config.fish

@@ -22,7 +22,7 @@ end
 
 # Commands to run in interactive sessions can go here
 if status is-interactive
-	if type -q atuin
+	if type -q atuin; and test -s ~/.local/share/atuin/key
 		atuin init fish --disable-up-arrow | source
 	end