[generic] prefer enclosures over following links in rss feeds
diff --git a/youtube_dl/extractor/generic.py b/youtube_dl/extractor/generic.py
index e3cb5c5ce51..c548a164907 100644
--- a/youtube_dl/extractor/generic.py
+++ b/youtube_dl/extractor/generic.py
@@ -190,6 +190,16 @@ class GenericIE(InfoExtractor):
                 'title': 'pdv_maddow_netcast_m4v-02-27-2015-201624',
             }
         },
+        # RSS feed with enclosures and unsupported link URLs
+        {
+            'url': 'http://www.hellointernet.fm/podcast?format=rss',
+            'info_dict': {
+                'id': 'http://www.hellointernet.fm/podcast?format=rss',
+                'description': 'CGP Grey and Brady Haran talk about YouTube, life, work, whatever.',
+                'title': 'Hello Internet',
+            },
+            'playlist_mincount': 100,
+        },
         # SMIL from http://videolectures.net/promogram_igor_mekjavic_eng
         {
             'url': 'http://videolectures.net/promogram_igor_mekjavic_eng/video/1/smil.xml',
@@ -2009,13 +2019,15 @@ def _extract_rss(self, url, video_id, doc):
 
         entries = []
         for it in doc.findall('./channel/item'):
-            next_url = xpath_text(it, 'link', fatal=False)
+            next_url = None
+            enclosure_nodes = it.findall('./enclosure')
+            for e in enclosure_nodes:
+                next_url = e.attrib.get('url')
+                if next_url:
+                    break
+
             if not next_url:
-                enclosure_nodes = it.findall('./enclosure')
-                for e in enclosure_nodes:
-                    next_url = e.attrib.get('url')
-                    if next_url:
-                        break
+                next_url = xpath_text(it, 'link', fatal=False)
 
             if not next_url:
                 continue

## Please follow the guide below

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---

### Before submitting a *pull request* make sure you have:
- [x] At least skimmed through [adding new extractor tutorial](https://github.com/rg3/youtube-dl#adding-support-for-a-new-site) and [youtube-dl coding conventions](https://github.com/rg3/youtube-dl#youtube-dl-coding-conventions) sections
- [x] [Searched](https://github.com/rg3/youtube-dl/search?q=is%3Apr&type=Issues) the bugtracker for similar pull requests
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### In order to be accepted and merged into youtube-dl each piece of code must be in public domain or released under [Unlicense](http://unlicense.org/). Check one of the following options:
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### What is the purpose of your *pull request*?
- [ ] Bug fix
- [x] Improvement
- [ ] New extractor
- [ ] New feature

---

### Description of your *pull request* and other information

When downloading from rss feeds, the generic extractor follows the rss links first. This leads to "ERROR: Unsupported URL" messages in a lot of cases. Even though there are enclosures present.

```
$ youtube-dl --playlist-end 1 http://www.hellointernet.fm/podcast?format=rss
[generic] podcast?format=rss: Requesting header
WARNING: Falling back on generic information extractor.
[generic] podcast?format=rss: Downloading webpage
[generic] podcast?format=rss: Extracting information
[download] Downloading playlist: Hello Internet
[generic] playlist Hello Internet: Collected 100 video ids (downloading 1 of them)
[download] Downloading video 1 of 1
[generic] onehundred: Requesting header
WARNING: Falling back on generic information extractor.
[generic] onehundred: Downloading webpage
[generic] onehundred: Extracting information
ERROR: Unsupported URL: http://www.hellointernet.fm/podcast/onehundred
```

With this pull request downloading enclosures is preferred over following the rss links.

```
$ python -m youtube_dl --playlist-end 1 http://www.hellointernet.fm/podcast?format=rss
[generic] podcast?format=rss: Requesting header
WARNING: Falling back on generic information extractor.
[generic] podcast?format=rss: Downloading webpage
[generic] podcast?format=rss: Extracting information
[download] Downloading playlist: Hello Internet
[generic] playlist Hello Internet: Collected 100 video ids (downloading 1 of them)
[download] Downloading video 1 of 1
[generic] Hello_Internet_Episode_One_Hundred: Requesting header
[redirect] Following redirect to http://hwcdn.libsyn.com/p/e/5/c/e5ca0f579a9f12b4/Hello_Internet_Episode_One_Hundred.mp3?c_id=20078576&expiration=1523726590&hwt=d00666280d294aea41062d82e934b6f0
[generic] Hello_Internet_Episode_One_Hundred: Requesting header
[download] Destination: Hello Internet Episode One Hundred-Hello_Internet_Episode_One_Hundred.mp3
[download] 100% of 96.39MiB in 00:09
[download] Finished downloading playlist: Hello Internet
```