fix rule34 api url, guard against non-list responses

downloader.py

@@ -55,7 +55,7 @@ SITES = {
         'post_url_fmt': 'https://yande.re/post/show/{post_id}',
     },
     'rule34': {
-        'base_url': 'https://rule34.xxx/',
+        'base_url': 'https://api.rule34.xxx/',
         'endpoint': 'index.php?page=dapi&s=post&q=index&json=1',
         'per_page': 100,
         'threads': 20,
@@ -83,6 +83,8 @@ def fetch_all_posts(adapter, query, auth, limit):
         r.raise_for_status()
         data = r.json()
         batch = data[adapter['envelope']] if adapter['envelope'] else data
+        if not isinstance(batch, list):
+            raise RuntimeError(f'API returned unexpected response: {batch!r}')
         if not batch:
             break
         posts.extend(batch)