Update wallpaper download jobs to be idempotent

bin/.bin/get_astrobin_potd.py

@@ -1,8 +1,17 @@
 #!/usr/bin/env python3
+import os
 from datetime import datetime
 import requests
 import subprocess
 
+today = datetime.today().strftime("%Y-%m-%d")
+target_path = f"/home/powellc/var/inbox/astrobin/{today}.jpg"
+
+# If the file for today already exists, just exit
+if os.path.isfile(target_path):
+    print(f"Astrobin image for {today} already exists, skipping download")
+    exit()
+
 root = "https://www.astrobin.com"
 api_key = "3f542cbb23407bde6f20490f377366582dd1a54c"
 api_secret = (
@@ -20,9 +29,6 @@ r = requests.get(
 image_uri = r.json()["url_real"]
 img = requests.get(image_uri, stream=True)
 
-today = datetime.today().strftime("%Y-%m-%d")
-target_path = f"/home/powellc/var/inbox/astrobin/{today}.jpg"
-
 handle = open(target_path, "wb")
 for chunk in img.iter_content(chunk_size=512):
     if chunk:  # filter out keep-alive new chunks