Gnu `[` evaluates both sides of a -o condition regardless

It doesn't short circuit like we expect, causing trouble when $dir is
empty

Use shell builtin instead

shell/completion.zsh

@@ -44,7 +44,7 @@ __fzf_generic_path_completion() {
   setopt localoptions nonomatch
   dir="$base"
   while [ 1 ]; do
-    if [ -z "$dir" -o -d ${~dir} ]; then
+    if [[ -z "$dir" || -d ${~dir} ]]; then
       leftover=${base/#"$dir"}
       leftover=${leftover/#\/}
       [ -z "$dir" ] && dir='.'