Make ownCloud work again in php 7.0.6

See https://bugs.php.net/bug.php?id=72117
Basically a bugfix in php caused this issue. So isset is not called more
often. We have to catch this.

lib/private/appframework/http/request.php

@@ -264,6 +264,9 @@ class Request implements \ArrayAccess, \Countable, IRequest {
 	 * @return bool
 	 */
 	public function __isset($name) {
+		if (in_array($name, $this->allowedKeys, true)) {
+			return true;
+		}
 		return isset($this->items['parameters'][$name]);
 	}