Fix warnings.

media_attribution.module

@@ -85,7 +85,7 @@ function media_attribution_preprocess_field__paragraph__field_attribution_author
 
 function media_attribution_preprocess_paragraph__license_attribution__license_attribution(&$variables) {
   $variables['license_prefix'] = \Drupal::translation()->translate('Licensed under');
-  $items = $variables['elements']['field_license']['#items'];
+  $items = isset($variables['elements']['field_license']['#items']) ? $variables['elements']['field_license']['#items'] : [];
   if (!empty($items)) {
     $referencedEntity = $variables['elements']['field_license']['#items']
       ->first()->get('entity')->getTarget()->getValue();
@@ -105,7 +105,8 @@ function media_attribution_preprocess_entity_embed_container(&$variables) {
       && $attributions = $variables['element']['#entity']->get('field_image_attribution')
       ->referencedEntities()) {
     $attribution = $attributions[0];
-    $author = $attribution->get('field_attribution_author')->getValue()[0];
+    $author_field = $attribution->get('field_attribution_author')->getValue();
+    $author = isset($author_field[0]) ? $author_field[0] : '';
 
     $source = $attribution->get('field_attribution_source')->count() > 0 ? $attribution->get('field_attribution_source')->getValue()[0] : '';
     $license = $attribution->get('field_license')->entity;