[reddit] add 'previews' option (#4322)

another way to disable this new behavior

docs/configuration.rst

@@ -2716,6 +2716,17 @@ Description
     Ignore all submissions posted before/after the submission with this ID.
 
 
+extractor.reddit.previews
+-------------------------
+Type
+    ``bool``
+Default
+    ``true``
+Description
+    For failed downloads from external URLs / child extractors,
+    download Reddit's preview image/video if available.
+
+
 extractor.reddit.recursion
 --------------------------
 Type

gallery_dl/extractor/reddit.py

@@ -30,6 +30,7 @@ class RedditExtractor(Extractor):
 
         parentdir = self.config("parent-directory")
         max_depth = self.config("recursion", 0)
+        previews = self.config("previews", True)
 
         videos = self.config("videos", True)
         if videos:
@@ -119,7 +120,7 @@ class RedditExtractor(Extractor):
                     if match:
                         extra.append(match.group(1))
                     elif not match_user(url) and not match_subreddit(url):
-                        if "preview" in data:
+                        if previews and "preview" in data:
                             data["_fallback"] = self._previews(data)
                         yield Message.Queue, text.unescape(url), data
                         if "_fallback" in data: