Fix strange wrapping of colon after topic type

The way I was doing this before had the colon as part of the metadata,
which meant that it could wrap onto the next line in thin windows,
giving a result like:

Article
: 1500 words

This changes it so that it's added with CSS after the content type when
needed, so it won't wrap separately.

tildes/scss/modules/_topic.scss

@@ -90,6 +90,12 @@
   margin-right: 0.4rem;
 }
 
+// Add a colon after the topic-content-type only when there's metadata after it
+.topic-content-type:not(:last-child)::after {
+  content: ": ";
+  margin-right: 0.2rem;
+}
+
 .topic-group {
   margin-right: 0.4rem;
 }

tildes/tildes/templates/macros/topics.jinja2

@@ -49,7 +49,7 @@
       <span class="topic-content-type">{{ topic.content_type.display_name if topic.content_type else "Link" }}</span>
 
       {% if topic.content_metadata_for_display %}
-        <span class="topic-content-metadata">: {{ topic.content_metadata_for_display }}</span>
+        <span class="topic-content-metadata">{{ topic.content_metadata_for_display }}</span>
       {% endif %}
 
       {% if topic.unimportant_tags and request.user and request.user.show_tags_in_listings %}