Fix #1920 (port #1918)

Author: gkorland

src/main/java/redis/clients/jedis/Jedis.java

@@ -3629,10 +3629,12 @@ public Map<String, String> pubsubNumSub(String... channels) {
   @Override
   public void close() {
     if (dataSource != null) {
+      Pool<Jedis> pool = this.dataSource;
+      this.dataSource = null;
       if (client.isBroken()) {
-        this.dataSource.returnBrokenResource(this);
+        pool.returnBrokenResource(this);
       } else {
-        this.dataSource.returnResource(this);
+        pool.returnResource(this);
       }
       this.dataSource = null;
     } else {