don't show org logo if it isn't set

Author: timwis

_layouts/dataset.html

@@ -17,7 +17,7 @@
       <div class="col-sm-3" property="dct:publisher" resource="{{ organization_url }}">
         <div class="panel panel-default">
             <div class="panel-heading">
-              {% if organization.logo != empty %}
+              {% if organization.logo and organization.logo != empty %}
               <a href="{{ site.baseurl }}/datasets/?organization={{ organization.title | slugify }}" class="thumbnail"><img src="{{ organization.logo }}" alt="{{ organization.title }} logo"></a>
               {% endif %}
             </div>

_layouts/organization.html

@@ -5,7 +5,7 @@
 
 <div data-component="view-switcher">
   <div class="row" data-hook="view" data-view="display">
-    {% if page.logo != empty %}
+    {% if page.logo and page.logo != empty %}
     <div class="col-sm-3">
       <a href="{{ page.logo }}" class="thumbnail"><img src="{{ page.logo }}" alt="{{ page.title }} logo"></a>
     </div>

organizations.html

@@ -11,7 +11,7 @@
   {% assign dataset_count = site.datasets | where:"organization", organization.title | size %}
   <div class="media">
     <div class="media-left">
-      {% if organization.logo != empty %}
+      {% if organization.logo and organization.logo != empty %}
         <a href="{{ site.baseurl }}{{ organization.url }}" class="organization-thumbnail">
           <img class="media-object" src="{{ organization.logo }}" alt="{{ organization.title }}">
         </a>