Fix admin readonly field performance. Close viewflow#345

Author: kmmbvnr

material/admin/templates/material/fields/django_adminreadonlyfield.html

@@ -1,22 +1,24 @@
 <div class="row">
-    {% if 'admin/img/icon-' in fieldset_field.contents %}
+    {% with contents=fieldset_field.contents %}
+    {% if 'admin/img/icon-' in contents %}
     <div class="checkbox-field col s12">
-        <input type="checkbox" id="test7" {% if 'icon-yes' in fieldset_field.contents %}checked="checked"{% endif %} disabled="disabled" />
+        <input type="checkbox" id="test7" {% if 'icon-yes' in contents %}checked="checked"{% endif %} disabled="disabled" />
         <label for="test7">{{ fieldset_field.field.label|title }}</label>
     </div>
     {% else %}
-    {% if '<' in fieldset_field.contents and '>' in fieldset_field.contents or fieldset_field.contents == "" %}
+    {% if '<' in contents and '>' in contents or contents == "" %}
         <div class="col s12">
-            {{ fieldset_field.contents }}
+            {{ contents }}
         </div>
         {% else %}
             <div class="input-field col s12">
                 <label class="active">{{ fieldset_field.field.label|title }}</label>
-                <input disabled value="{{ fieldset_field.contents }}">
+                <input disabled value="{{ contents }}">
                 {% if fieldset_field.field.help_text %}
                     <div class="help-block">{{ fieldset_field.field.help_text|safe }}</div>
                 {% endif %}
             </div>
          {% endif %}
     {% endif %}
+    {% endwith %}
 </div>