builer/virtualbox: avoid crash since guest additions path not set

builder/virtualbox/step_attach_guest_additions.go

@@ -25,7 +25,6 @@ type stepAttachGuestAdditions struct {
 func (s *stepAttachGuestAdditions) Run(state multistep.StateBag) multistep.StepAction {
 	config := state.Get("config").(*config)
 	driver := state.Get("driver").(Driver)
-	guestAdditionsPath := state.Get("guest_additions_path").(string)
 	ui := state.Get("ui").(packer.Ui)
 	vmName := state.Get("vmName").(string)
 
@@ -35,6 +34,9 @@ func (s *stepAttachGuestAdditions) Run(state multistep.StateBag) multistep.StepA
 		return multistep.ActionContinue
 	}
 
+	// Get the guest additions path since we're doing it
+	guestAdditionsPath := state.Get("guest_additions_path").(string)
+
 	// Attach the guest additions to the computer
 	log.Println("Attaching guest additions ISO onto IDE controller...")
 	command := []string{

builder/virtualbox/step_upload_guest_additions.go

@@ -19,7 +19,6 @@ func (s *stepUploadGuestAdditions) Run(state multistep.StateBag) multistep.StepA
 	comm := state.Get("communicator").(packer.Communicator)
 	config := state.Get("config").(*config)
 	driver := state.Get("driver").(Driver)
-	guestAdditionsPath := state.Get("guest_additions_path").(string)
 	ui := state.Get("ui").(packer.Ui)
 
 	// If we're attaching then don't do this, since we attached.
@@ -28,6 +27,9 @@ func (s *stepUploadGuestAdditions) Run(state multistep.StateBag) multistep.StepA
 		return multistep.ActionContinue
 	}
 
+	// Get the guest additions path since we're doing it
+	guestAdditionsPath := state.Get("guest_additions_path").(string)
+
 	version, err := driver.Version()
 	if err != nil {
 		state.Put("error", fmt.Errorf("Error reading version for guest additions upload: %s", err))