[zsh] Fix up init functions

- Use autoload +X in do_init_functions
- Properly redirect stdout and stderr in do_init_functions and init_env_vi so
  they don't print anything

zsh/func/do_init_functions

@@ -2,7 +2,7 @@
 # Eryn Wells <eryn@erynwells.me>
 
 for func in ${(P)${1}}; do
-    if autoload -Uz $func >& -; then
+    if autoload +X -Uz $func &> /dev/null; then
         $func
     fi
 done