[fix] ResultContainer: use self._lock and self._closed for all properties

Close #3474

searx/results.py

@@ -430,6 +430,11 @@ class ResultContainer:
         """Returns the average of results number, returns zero if the average
         result number is smaller than the actual result count."""
 
+        with self._lock:
+            if not self._closed:
+                logger.error("call to ResultContainer.number_of_results before ResultContainer.close")
+                return 0
+
             resultnum_sum = sum(self._number_of_results)
             if not resultnum_sum or not self._number_of_results:
                 return 0
@@ -440,11 +445,23 @@ class ResultContainer:
             return average
 
     def add_unresponsive_engine(self, engine_name: str, error_type: str, suspended: bool = False):
+        with self._lock:
+            if self._closed:
+                logger.error("call to ResultContainer.add_unresponsive_engine after ResultContainer.close")
+                return
             if engines[engine_name].display_error_messages:
                 self.unresponsive_engines.add(UnresponsiveEngine(engine_name, error_type, suspended))
 
     def add_timing(self, engine_name: str, engine_time: float, page_load_time: float):
+        with self._lock:
+            if self._closed:
+                logger.error("call to ResultContainer.add_timing after ResultContainer.close")
+                return
             self.timings.append(Timing(engine_name, total=engine_time, load=page_load_time))
 
     def get_timings(self):
+        with self._lock:
+            if not self._closed:
+                logger.error("call to ResultContainer.get_timings before ResultContainer.close")
+                return []
             return self.timings