Fix the bug of misplaced locks in ContextUtil and ClusterNode (#1429)

- which may lead to IllegalMonitorStateException in unlock() when unchecked error occurs during lock()

sentinel-core/src/main/java/com/alibaba/csp/sentinel/context/ContextUtil.java

@@ -127,8 +127,8 @@ public class ContextUtil {
                     setNullContext();
                     return NULL_CONTEXT;
                 } else {
+                    LOCK.lock();
                     try {
-                        LOCK.lock();
                         node = contextNameNodeMap.get(name);
                         if (node == null) {
                             if (contextNameNodeMap.size() > Constants.MAX_CONTEXT_NAME_SIZE) {

sentinel-core/src/main/java/com/alibaba/csp/sentinel/node/ClusterNode.java

@@ -101,8 +101,8 @@ public class ClusterNode extends StatisticNode {
     public Node getOrCreateOriginNode(String origin) {
         StatisticNode statisticNode = originCountMap.get(origin);
         if (statisticNode == null) {
+            lock.lock();
             try {
-                lock.lock();
                 statisticNode = originCountMap.get(origin);
                 if (statisticNode == null) {
                     // The node is absent, create a new node for the origin.