people: Hide images when they don't exist

This commit updates the people_list page and people template to handle
cases where a specific person does not have an assoicated image.

_includes/people_list.html

@@ -14,7 +14,7 @@
             <h5>{{role.name}}(s)</h5></li>
             {% for person in rollers %}
                 <li class="collection-item avatar">
-                    <img src="/{{person.pic}}" alt="" class="circle"/>
+                    {% if person.pic %}<img src="/{{person.pic}}" alt="" class="circle"/>{% endif %}
                     <a href="{{person.url}}" class="title">{{person.fullname}}</a>
                     <p>
                       {% if person.start_date %}

_layouts/person.html

@@ -9,7 +9,9 @@ layout: default
     <div class="col s12 m5 right">
         <div class="card">
             <div class="card-image">
-                <img src="/{{page.pic}}" width="300"/>
+                {% if page.pic %}
+                    <img src="/{{page.pic}}" width="300"/>
+                {% endif %}
             </div>
             <div class="card-content">
                 <span class="card-title">{{ page.fullname }}</span>