fix: don't return null for SharedStorage::getWrapperStorage with share recursion

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

apps/files_sharing/lib/SharedStorage.php

@@ -137,6 +137,16 @@ class SharedStorage extends \OC\Files\Storage\Wrapper\Jail implements ISharedSto
 
 	private function init() {
 		if ($this->initialized) {
+			if (!$this->storage) {
+				// marked as initialized but no storage set
+				// this is probably because some code path has caused recursion during the share setup
+				// we setup a "failed storage" so `getWrapperStorage` doesn't return null.
+				// If the share setup completes after this the "failed storage" will be overwritten by the correct one
+				$this->logger->warning('Possible share setup recursion detected');
+				$this->storage = new FailedStorage(['exception' => new \Exception('Possible share setup recursion detected')]);
+				$this->cache = new FailedCache();
+				$this->rootPath = '';
+			}
 			return;
 		}