Return 1 when GNU Core Utilities are not found

plugins/gnu-utils/init.zsh

@@ -5,7 +5,11 @@
 #   Sorin Ionescu <sorin.ionescu@gmail.com>
 #
 
-if (( $+commands[gdircolors] )); then
+# Check for the presence of GNU Core Utilities.
+if (( ! $+commands[gdircolors] )); then
+  return 1
+fi
+
 function __gnu_utils {
   emulate -L zsh
   local gcmds
@@ -70,5 +74,4 @@ if (( $+commands[gdircolors] )); then
 else
   alias ls="$aliases[ls] -F"
 fi
-fi