abstract_replication_strategy: work around missing _snitch in cql_query_test

locator/abstract_replication_strategy.hh

@@ -33,7 +33,13 @@ public:
     virtual ~abstract_replication_strategy() {}
     static std::unique_ptr<abstract_replication_strategy> create_replication_strategy(const sstring& ks_name, const sstring& strategy_name, token_metadata& token_metadata, snitch_ptr&& snitch, const std::map<sstring, sstring>& config_options);
     std::vector<inet_address> get_natural_endpoints(const token& search_token);
-    future<> stop() { return _snitch->stop(); }
+    future<> stop() {
+        if (_snitch) {
+            return _snitch->stop();
+        } else {
+            return make_ready_future<>();
+        }
+    }
     virtual size_t get_replication_factor() const = 0;
 };