Less error-prone enclosure_length getting

Signed-off-by: Chris Warrick <kwpolska@gmail.com>

CHANGES.txt

@@ -4,6 +4,7 @@ New in master
 Features
 --------
 
+* Added ``enclosure_length`` meta field for better interop (Issue #2338)
 * New Lithuanian translation by Antanas Lasys
 
 Bugfixes

nikola/nikola.py

@@ -295,7 +295,13 @@ def _enclosure(post, lang):
     """Add an enclosure to RSS."""
     enclosure = post.meta('enclosure', lang)
     if enclosure:
-        length = int(post.meta('enclosure_length', lang) or 0)
+        try:
+            length = int(post.meta('enclosure_length', lang) or 0)
+        except KeyError:
+            length = 0
+        except ValueError:
+            utils.LOGGER.warn("Invalid enclosure length for post {0}".format(post.source_path))
+            length = 0
         url = enclosure
         mime = mimetypes.guess_type(url)[0]
         return url, length, mime

tests/test_rss_feeds.py

@@ -56,7 +56,8 @@ def setUp(self):
                               'tags': 'tags',
                               'link': 'link',
                               'description': 'description',
-                              'enclosure': 'http://www.example.org/foo.mp3'},
+                              'enclosure': 'http://www.example.org/foo.mp3',
+                              'enclosure_length': '5'},
                              True)
                         ))):
             with mock.patch('nikola.nikola.utils.os.path.isdir',