advanced-search: panel is visible when checked before

searx/search.py

         self.pageno = 1
         self.lang = 'all'
         self.time_range = None
+        self.is_advanced = None
 
         # set blocked engines
         self.disabled_engines = request.preferences.engines.get_disabled()
             self.lang = query_obj.languages[-1]
 
         self.time_range = self.request_data.get('time_range')
+        self.is_advanced = self.request_data.get('advanced_search')
 
         self.engines = query_obj.engines
 
             # 0 = None, 1 = Moderate, 2 = Strict
             request_params['safesearch'] = request.preferences.get_value('safesearch')
             request_params['time_range'] = self.time_range
+            request_params['advanced_search'] = self.is_advanced
 
             # update request parameters dependent on
             # search-engine (contained in engines folder)

searx/templates/oscar/advanced.html

 <div class="input-group col-sm-12 advanced">
-    <input type="checkbox" id="check-advanced">
+    <input type="checkbox" name="advanced_search" id="check-advanced" {% if advanced_search %} checked="checked"{% endif %}>
     <label for="check-advanced">
         <span class="glyphicon glyphicon-cog"></span>
         {{ _('Advanced settings') }}

searx/webapp.py

         paging=search.paging,
         number_of_results=format_decimal(number_of_results),
         pageno=search.pageno,
+        advanced_search=search.is_advanced,
         time_range=search.time_range,
         base_url=get_base_url(),
         suggestions=search.result_container.suggestions,