fish_vi_cursor: Check for tput before using

If tput isn't available, that's the same as if it failed.

This is the last bit necessary to make the tests work on alpine on builds.sr.ht.

share/functions/fish_vi_cursor.fish

@@ -32,7 +32,7 @@ function fish_vi_cursor -d 'Set cursor shape for different vi modes'
     # We use the `tput` here just to see if terminfo thinks we can change the cursor.
     # We cannot use that sequence directly as it's not the correct one for konsole and iTerm,
     # and because we may want to change the cursor even though terminfo says we can't (tmux).
-    if not tput Ss >/dev/null 2>/dev/null
+    if begin; not command -sq tput; or not tput Ss >/dev/null 2>/dev/null; end
         # Whitelist tmux...
         and not begin
             set -q TMUX