fix error handling, null URLs in templates, and Radio playlist support

- Global error handler: friendly messages for 429, 502, 403, 400
  instead of raw tracebacks. Filter FetchError from Flask logger.
- Fix None URLs in templates: protect href/src in common_elements,
  playlist, watch, and comments templates against None values.
- Radio playlists (RD...): redirect /playlist?list=RD... to
  /watch?v=...&list=RD... since YouTube only supports them in player.
- Wrap player client fallbacks (ios, tv_embedded) in try/catch so
  a failed fallback doesn't crash the whole page.

youtube/templates/comments.html

@@ -3,13 +3,13 @@
 {% macro render_comment(comment, include_avatar, timestamp_links=False) %}
     <div class="comment-container">
         <div class="comment">
-            <a class="author-avatar" href="{{ comment['author_url'] }}" title="{{ comment['author'] }}">
+            <a class="author-avatar" href="{{ comment['author_url'] or '#' }}" title="{{ comment['author'] }}">
                 {% if include_avatar %}
                     <img class="author-avatar-img" alt="{{ comment['author'] }}" src="{{ comment['author_avatar'] }}">
                 {% endif %}
             </a>
             <address class="author-name">
-                <a class="author" href="{{ comment['author_url'] }}" title="{{ comment['author'] }}">{{ comment['author'] }}</a>
+                <a class="author" href="{{ comment['author_url'] or '#' }}" title="{{ comment['author'] }}">{{ comment['author'] }}</a>
             </address>
             <a class="permalink" href="{{ comment['permalink'] }}" title="permalink">
                 <span>{{ comment['time_published'] }}</span>

youtube/templates/common_elements.html

@@ -20,7 +20,7 @@
             {{ info['error'] }}
         {% else %}
             <div class="item-video {{ info['type'] + '-item' }}">
-                <a class="thumbnail-box" href="{{ info['url'] }}" title="{{ info['title'] }}">
+                <a class="thumbnail-box" href="{{ info['url'] or '#' }}" title="{{ info['title'] }}">
                     <div class="thumbnail {% if info['type'] == 'channel' %} channel {% endif %}">
                         {% if lazy_load %}
                             <img class="thumbnail-img lazy" alt="&#x20;" data-src="{{ info['thumbnail'] }}" onerror="thumbnail_fallback(this)">
@@ -35,7 +35,7 @@
                         {% endif %}
                     </div>
                 </a>
-                <h4 class="title"><a href="{{ info['url'] }}" title="{{ info['title'] }}">{{ info['title'] }}</a></h4>
+                <h4 class="title"><a href="{{ info['url'] or '#' }}" title="{{ info['title'] }}">{{ info['title'] }}</a></h4>
 
                 {% if include_author %}
                     {% set author_description = info['author'] %}

youtube/templates/playlist.html

@@ -10,11 +10,17 @@
 
     <div class="playlist-metadata">
         <div class="author">
+            {% if thumbnail %}
             <img alt="{{ title }}" src="{{ thumbnail }}">
+            {% endif %}
             <h2>{{ title }}</h2>
         </div>
         <div class="summary">
+            {% if author_url %}
             <a class="playlist-author" href="{{ author_url }}">{{ author }}</a>
+            {% else %}
+            <span class="playlist-author">{{ author }}</span>
+            {% endif %}
         </div>
         <div class="playlist-stats">
             <div>{{ video_count|commatize }} videos</div>

youtube/templates/watch.html

@@ -172,7 +172,11 @@
                             {% else %}
                                 <li>{{ playlist['current_index']+1 }}/{{ playlist['video_count'] }}</li>
                             {% endif %}
+                            {% if playlist['author_url'] %}
                             <li><a href="{{ playlist['author_url'] }}" title="{{ playlist['author'] }}">{{ playlist['author'] }}</a></li>
+                            {% elif playlist['author'] %}
+                            <li>{{ playlist['author'] }}</li>
+                            {% endif %}
                         </ul>
                     </div>
                     <nav class="playlist-videos">