hocr Islandora IIIF: Add missing null check.

modules/islandora_iiif/src/Plugin/views/style/IIIFManifest.php

@@ -423,9 +423,11 @@ class IIIFManifest extends StylePluginBase {
       if (!is_null($ocr_field_name)) {
         $ocrs = $ocr_entity->{$ocr_field_name};
         $ocr = $ocrs[0] ?? FALSE;
+        if ($ocr) {
           $ocr_url = $ocr->entity->createFileUrl(FALSE);
         }
       }
+    }
     elseif ($structured_text_term = $this->getStructuredTextTerm()) {
       $parent_node = $this->utils->getParentNode($entity);
       $ocr_entity_array = $this->utils->getMediaReferencingNodeAndTerm($parent_node, $structured_text_term);