Return false in hasUpdated when storage is not available

Technically, saying that a storage has no updates when it's not
available is correct.

This makes it possible to retrieve the cache entry for the mount point
and also to list and remove unavailable federated shares.

Signed-off-by: Vincent Petry <vincent@nextcloud.com>

lib/private/Files/Storage/Wrapper/Availability.php

@@ -379,11 +379,15 @@ class Availability extends Wrapper {
 
 	/** {@inheritdoc} */
 	public function hasUpdated($path, $time) {
-		$this->checkAvailability();
+		if (!$this->isAvailable()) {
+			return false;
+		}
 		try {
 			return parent::hasUpdated($path, $time);
 		} catch (StorageNotAvailableException $e) {
-			$this->setUnavailable($e);
+			// set unavailable but don't rethrow
+			$this->setUnavailable(null);
+			return false;
 		}
 	}
 
@@ -449,7 +453,7 @@ class Availability extends Wrapper {
 	/**
 	 * @throws StorageNotAvailableException
 	 */
-	protected function setUnavailable(StorageNotAvailableException $e) {
+	protected function setUnavailable(?StorageNotAvailableException $e) {
 		$delay = self::RECHECK_TTL_SEC;
 		if ($e instanceof StorageAuthException) {
 			$delay = max(
@@ -459,7 +463,9 @@ class Availability extends Wrapper {
 			);
 		}
 		$this->getStorageCache()->setAvailability(false, $delay);
-		throw $e;
+		if ($e !== null) {
+			throw $e;
+		}
 	}