Merge pull request #22943 from owncloud/backport-22800-stable9

[9.0] don't hide server not available exception, fixes #20536

lib/base.php

@@ -716,6 +716,9 @@ class OC {
 				try {
 					$cache = new \OC\Cache\File();
 					$cache->gc();
+				} catch (\OC\ServerNotAvailableException $e) {
+					// not a GC exception, pass it on
+					throw $e;
 				} catch (\Exception $e) {
 					// a GC exception should not prevent users from using OC,
 					// so log the exception