fix npe

fine-druid/src/com/fr/third/alibaba/druid/pool/DruidDataSource.java

@@ -613,6 +613,12 @@ public class DruidDataSource extends DruidAbstractDataSource implements DruidDat
     }
 
     private void checkThread() throws SQLException {
+        if (createConnectionThread == null){
+            throw new IllegalStateException("createConnectionThread not start!");
+        }
+        if (destroyConnectionThread == null){
+            throw new IllegalStateException("destroyConnectionThread not start!");
+        }
         if (!createConnectionThread.isStarted() && !destroyConnectionThread.isStarted()) {
             synchronized (this) {//线程安全问题，加个双检锁
                 if (!createConnectionThread.isStarted() && !destroyConnectionThread.isStarted()) {
@@ -2152,8 +2158,8 @@ public class DruidDataSource extends DruidAbstractDataSource implements DruidDat
 
                         try {
                             Thread.sleep(timeBetweenConnectErrorMillis);
-                        } catch (InterruptedException interruptEx) {
-                            break;
+                        } catch (InterruptedException ignore) {
+
                         }
                         DruidDataSource.this.createThreadChange();
                         break;