cal: check if image exists before downloading

lumbunglib/cloudcal.py

@@ -146,6 +146,7 @@ def create_event_post(post_dir, event):
         if not os.path.exists(local_image):
             # download preview image
             response = requests.get(img, stream=True)
+            if response.status_code == 200:
                 with open(local_image, "wb") as img_file:
                     shutil.copyfileobj(response.raw, img_file)
                     print('Downloaded image for event "{}"'.format(event.name))