Extract component to render poll geozones

This way we remove a bit of duplication.

These changes also affect the way geozones are rendered in a couple of
minor ways, making them more consistent:

* No empty list of geozones is rendered when there are no geozones
  (before these changes, an empty list was rendered in the index action
  but not in the show action)
* The text clarifying the geozone restriction is always shown (before
  these changes, it was shown in the index action but not in the show
  action)

We've added tests for these cases.

app/components/polls/geozones_component.html.erb

@@ -0,0 +1,9 @@
+<p>
+  <small><%= t("polls.index.geozone_info") %></small>
+</p>
+
+<ul class="tags">
+  <% poll.geozones.each do |geozone| %>
+    <li><span><%= geozone.name %></span></li>
+  <% end %>
+</ul>

app/components/polls/geozones_component.rb

@@ -0,0 +1,11 @@
+class Polls::GeozonesComponent < ApplicationComponent
+  attr_reader :poll
+
+  def initialize(poll)
+    @poll = poll
+  end
+
+  def render?
+    poll.geozones.any?
+  end
+end

app/components/polls/poll_component.html.erb

@@ -40,16 +40,7 @@
           <% end %>
         </ul>
       <% end %>
-      <% if poll.geozones.any? %>
-        <p>
-          <small><%= t("polls.index.geozone_info") %></small>
-        </p>
-      <% end %>
-      <ul class="tags">
-        <% poll.geozones.each do |g| %>
-          <li><span><%= g.name %></span></li>
-        <% end %>
-      </ul>
+      <%= render Polls::GeozonesComponent.new(poll) %>
       <%= render SDG::TagListComponent.new(poll, limit: 5, linkable: false) %>
     </div>
     <div class="small-12 medium-3 column table" data-equalizer-watch>

app/components/polls/poll_header_component.html.erb

@@ -11,13 +11,7 @@
 
       <%= auto_link_already_sanitized_html simple_format(poll.summary) %>
 
-      <% if poll.geozones.any? %>
-        <ul class="margin-top tags">
-          <% poll.geozones.each do |g| %>
-            <li><span><%= g.name %></span></li>
-          <% end %>
-        </ul>
-      <% end %>
+      <%= render Polls::GeozonesComponent.new(poll) %>
       <%= render SDG::TagListComponent.new(poll, linkable: false) %>
     </div>