composer: keep composer autocompletion when using global (#5933)

plugins/composer/composer.plugin.zsh

@@ -18,17 +18,13 @@ _composer () {
     local curcontext="$curcontext" state line
     typeset -A opt_args
     _arguments \
-    '1: :->command'\
-    '*: :->args'
+        '*:: :->subcmds'
 
-  case $state in
-    command)
+    if (( CURRENT == 1 )) || ( ((CURRENT == 2)) && [ "$words[1]" = "global" ] ) ; then
         compadd $(_composer_get_command_list)
-      ;;
-    *)
+    else
         compadd $(_composer_get_required_list)
-      ;;
-  esac
+    fi
 }
 
 compdef _composer composer