Merge pull request #14694 from nextcloud/backport/14684/stable15

[stable15] handle long etags from dav external storage

lib/private/Files/Storage/DAV.php

@@ -726,7 +726,11 @@ class DAV extends Common {
 			return null;
 		}
 		if (isset($response['{DAV:}getetag'])) {
-			return trim($response['{DAV:}getetag'], '"');
+			$etag = trim($response['{DAV:}getetag'], '"');
+			if (strlen($etag) > 40) {
+				$etag = md5($etag);
+			}
+			return $etag;
 		}
 		return parent::getEtag($path);
 	}