Fix 404 handling of requested JSON/XML

If front-end or an application requests JSON/XML, there is no point in
redirecting to the default page if that response doesn't exist. In the
worst case that would just cause another request, therefore server load,
traffic and a response that is meaningless to the requester.

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

lib/base.php

@@ -1048,6 +1048,13 @@ class OC {
 			return;
 		}
 
+		// Handle requests for JSON or XML
+		$acceptHeader = $request->getHeader('Accept');
+		if (in_array($acceptHeader, ['application/json', 'application/xml'], true)) {
+			http_response_code(404);
+			return;
+		}
+
 		// Someone is logged in
 		if (\OC::$server->getUserSession()->isLoggedIn()) {
 			OC_App::loadApps();