Alter field formatter settings even if settings form is empty

There should be no problem to invoke hook_field_formatter_settings_form_alter for empty settings-forms.

My consideration was, that there should not be a settings alter if there is no hook_field_formatter_settings_form implementation. In other words something that does not exist could not be altered, could it? I guess it's more a theoretical/philosophical consideration then practical.

I also had the problem that I wanted to alter a non existing settings-form, so I had to declare it in may custom module like:

if (!function_exists('xyz_field_formatter_settings_form') {
  function xyz_field_formatter_settings_form($form, $form_state) {
  }
}

In the end, if it is fine to call a alter-function for something that in first place does not exist, then I am fine with #2.

interdiff ctools-alter_empty_settings_forms-2537980-2.patch ctools-alter_empty_settings_forms-2537980-7.patch says:

--- b/includes/fields.inc
+++ b/includes/fields.inc
@@ -80,7 +80,7 @@
   if (function_exists($function)) {
     $settings_form = $function($field, $instance, $view_mode, $form, $form_state);
   }
-  if(!$settings_form) {
+  if (!isset($settings_form) || !$settings_form) {
     $settings_form = array();
   }

instead of if (!isset($settings_form) || !$settings_form) { we may use if (empty($settings_form)) {.