fix: add extra check to ensure wrapped shared storage is set

Signed-off-by: Robin Appelman <robin@icewind.nl>

Author: icewind1991

apps/files_sharing/lib/SharedStorage.php

@@ -569,6 +569,13 @@ public function getSourceStorage() {
 
 	public function getWrapperStorage() {
 		$this->init();
+
+		if (!$this->storage) {
+			$message = "no storage set after init for share " . $this->getShareId();
+			$this->logger->error($message);
+			$this->storage = new FailedStorage(['exception' => new \Exception($message)]);
+		}
+
 		return $this->storage;
 	}