show ligand_id if Xray data selected

problem raised in #204

ippisite/ippidb/templates/compound_form_content.html

@@ -41,7 +41,7 @@
                     {{form.common_name.label}}
                 </label>
             </div>
-            {%if form.is_a_ligand != None %}
+            {%if form.show_is_a_ligand != None %}
             <div class="input-inline">
                 <input type="text" name="{{form.ligand_id.html_name}}"
                     {%if form.ligand_id.value %}value="{{form.ligand_id.value}}" {%endif%}