Only cache terms that exist (Islandora#2272)

src/IslandoraUtils.php

@@ -301,14 +301,13 @@ class IslandoraUtils {
     if (!empty($results)) {
       $term = $this->entityTypeManager->getStorage('taxonomy_term')
         ->load(reset($results));
-    }
-
       $this->cache->set(
         $cid,
         $term,
         CacheBackendInterface::CACHE_PERMANENT,
         Cache::mergeTags(array_merge($term->getCacheTags(), ['user:' . $this->currentUser->id()]))
       );
+    }
 
     return $term;
   }