[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

zsh/func/init_env_vi

@@ -3,10 +3,10 @@
 
 # Prefer nvim and vim, in that order, over standard vi, which is insufferable.
 
-if whence -cp nvim >& -; then
+if whence -cp nvim &> /dev/null; then
     alias vi=nvim
     export EDITOR=nvim
-elif whence -cp vim >& -; then
+elif whence -cp vim &> /dev/null; then
     alias vi=vim
     export EDITOR=vim
 fi