Only preview notification text for valid media types

data/interfaces/default/notifier_text_preview.html

@@ -1,4 +1,3 @@
-% if text:
 <div class="modal-dialog" role="document">
     <div class="modal-content">
         <div class="modal-header">
@@ -6,6 +5,7 @@
             <h4 class="modal-title">Notification Text Preview</h4>
         </div>
         <div class="modal-body">
+            % if text:
             % for item in text:
             <div style="padding-bottom: 10px;">
                 <h4>${item['media_type'].capitalize()}</h4>
@@ -15,9 +15,11 @@
                 % endif
             </div>
             % endfor
+            % else:
+            <div style="text-align: center;"><i class="fa fa-exclamation-circle"></i> Failed to generate preview.</div>
+            % endif
         </div>
         <div class="modal-footer">
         </div>
     </div>
-</div>
-% endif
+</div>