command: root early handler func special case

This allows for early initialisation with access to flags on the root node. This can be useful for configuring global state used by subcommands.

Signed-off-by: Ophestra <cat@gensokyo.uk>

command/builder_test.go

@@ -7,7 +7,7 @@ import (
 )
 
 func TestBuild(t *testing.T) {
-	c := command.New(nil, nil, "test")
+	c := command.New(nil, nil, "test", nil)
 	stubHandler := func([]string) error { panic("unreachable") }
 
 	t.Run("nil direct handler", func(t *testing.T) {