[gnome-shell] extensionSystem: Check if extension exists before accessing property

[Florian Müllner <fmuellner src gnome org>]

commit e76877c4b889590251fb9b646e7283480979e089
Author: Jonas Dreßler <verdre v0yd nl>
Date:   Wed Sep 11 14:36:18 2019 +0200

    extensionSystem: Check if extension exists before accessing property
    
    If the extension doesn't exist in the `this._extensions` Map, we'd try
    to access `extension.dir` on undefined/null. So set the `dir` variable
    after checking if `extension` is defined.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/96

 js/ui/extensionSystem.js | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)
---
diff --git a/js/ui/extensionSystem.js b/js/ui/extensionSystem.js
index 47750bda38..98ef13be97 100644
--- a/js/ui/extensionSystem.js
+++ b/js/ui/extensionSystem.js
@@ -303,11 +303,10 @@ var ExtensionManager = class {
 
     _callExtensionInit(uuid) {
         let extension = this.lookup(uuid);
-        let dir = extension.dir;
-
         if (!extension)
             throw new Error("Extension was not properly created. Call createExtensionObject first");
 
+        let dir = extension.dir;
         let extensionJs = dir.get_child('extension.js');
         if (!extensionJs.query_exists(null)) {
             this.logExtensionError(uuid, new Error('Missing extension.js'));