views: fix client update form crashing

Fix client update view crashing due to missing images variable.

Check if GET /images fails.

ogcp/views.py

@@ -1009,6 +1009,12 @@ def action_client_update():
         if setup and setup[0].get('code') == 'MSDOS':
             setup[0]['code'] = 'MBR'
 
+        r = server.get('/images')
+        if r.status_code != requests.codes.ok:
+            flash(_('ogServer: error retrieving images list'),
+                  category='error')
+            return redirect(url_for('scopes'))
+        images = r.json()['images']
         for entry in setup:
             if images and entry['image'] != 0:
                 image = next((img for img in images if img['id'] == entry['image']), None)