[tagesschau] add support for more video types

I found that currently only tagesschau videos are played. There are some
more shows hosted on tagesschau.de (see [0] for example) which are
easily playable by adjusting the regex. So this patch adds support for:
* tagesthemen
* tagesschau vor 20 Jahren
* tagesschau (mit Gebärdensprache)
* nachtmagazin

Note that some videos don't provide a description, so in order for the
tests to succeed, an ExtractorError needs to get caught.

[0]: http://www.tagesschau.de/multimedia/video/videoarchiv2~_date-20150714.html

youtube_dl/extractor/tagesschau.py

@@ -4,11 +4,11 @@
 import re
 
 from .common import InfoExtractor
-from ..utils import parse_filesize
+from ..utils import parse_filesize, ExtractorError
 
 
 class TagesschauIE(InfoExtractor):
-    _VALID_URL = r'https?://(?:www\.)?tagesschau\.de/multimedia/(?:sendung/ts|video/video)(?P<id>-?[0-9]+)\.html'
+    _VALID_URL = r'https?://(?:www\.)?tagesschau\.de/multimedia/(?:sendung/(ts|tsg|tt|nm)|video/video|tsvorzwanzig)(?P<id>-?[0-9]+)\.html'
 
     _TESTS = [{
         'url': 'http://www.tagesschau.de/multimedia/video/video1399128.html',
@@ -30,6 +30,46 @@ class TagesschauIE(InfoExtractor):
             'title': 'Sendung: tagesschau \t04.12.2014 20:00 Uhr',
             'thumbnail': 're:^http:.*\.jpg$',
         }
+    }, {
+        'url': 'http://www.tagesschau.de/multimedia/sendung/tsg-3771.html',
+        'md5': '90757268b49ef56deae90c7b48928d58',
+        'info_dict': {
+            'id': '3771',
+            'ext': 'mp4',
+            'description': '',
+            'title': 'Sendung: tagesschau (mit Gebärdensprache) \t14.07.2015 20:00 Uhr',
+            'thumbnail': 're:^http:.*\.jpg$',
+        }
+    }, {
+        'url': 'http://www.tagesschau.de/multimedia/sendung/tt-3827.html',
+        'md5': '6e3ebdc75e8d67da966a8d06721eda71',
+        'info_dict': {
+            'id': '3827',
+            'ext': 'mp4',
+            'description': 'md5:d511d0e278b0ad341a95ad9ab992ce66',
+            'title': 'Sendung: tagesthemen \t14.07.2015 22:15 Uhr',
+            'thumbnail': 're:^http:.*\.jpg$',
+        }
+    }, {
+        'url': 'http://www.tagesschau.de/multimedia/sendung/nm-3475.html',
+        'md5': '8a8875a568f0a5ae5ceef93c501a225f',
+        'info_dict': {
+            'id': '3475',
+            'ext': 'mp4',
+            'description': 'md5:ed149f5649cda3dac86813a9d777e131',
+            'title': 'Sendung: nachtmagazin \t15.07.2015 00:15 Uhr',
+            'thumbnail': 're:^http:.*\.jpg$',
+        }
+    }, {
+        'url': 'http://www.tagesschau.de/multimedia/tsvorzwanzig-959.html',
+        'md5': 'be4d6f0421f2acd8abe25ea29f6f015b',
+        'info_dict': {
+            'id': '959',
+            'ext': 'mp4',
+            'description': '',
+            'title': 'Sendung: tagesschau vor 20 Jahren \t14.07.2015 22:45 Uhr',
+            'thumbnail': 're:^http:.*\.jpg$',
+        }
     }]
 
     _FORMATS = {
@@ -102,9 +142,14 @@ def _real_extract(self, url):
             thumbnail_fn = self._search_regex(
                 r'(?s)<img alt="Sendungsbild".*?src="([^"]+)"',
                 webpage, 'thumbnail', fatal=False)
+            # there are some videos without description
+            description = ""
+            try:
                 description = self._html_search_regex(
                     r'(?s)<p class="teasertext">(.*?)</p>',
                     webpage, 'description', fatal=False)
+            except ExtractorError:
+                pass
             title = self._html_search_regex(
                 r'<span class="headline".*?>(.*?)</span>', webpage, 'title')