Fix the cluster rule checking logic in FlowRuleUtil#checkClusterField() (#1105)

sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/block/flow/FlowRuleUtil.java

@@ -195,7 +195,7 @@ public final class FlowRuleUtil {
         if (!isWindowConfigValid(clusterConfig.getSampleCount(), clusterConfig.getWindowIntervalMs())) {
             return false;
         }
-        switch (rule.getStrategy()) {
+        switch (clusterConfig.getStrategy()) {
             case ClusterRuleConstant.FLOW_CLUSTER_STRATEGY_NORMAL:
                 return true;
             default: