连接池连接数量一直增加，超过maxActive

场景：
我的web应用使用了druid1.1.9版本，数据库mysql，应用要访问mysql中的mydb，当我先启动应用，再创建mysql database时，会触发这个问题，用netstat -anp|grep 3306，能够看到连接数一致在涨。

问题复现步骤：
启动web应用----》在mysql中创建test_db不创建表---》观察连接数一致在涨

Reproduce the issue with Druid 1.1.9 and MySQL by starting the web application before creating test_db without tables. Monitor port 3306 with netstat and compare the connection count with maxActive; done means the count no longer keeps increasing after the database is created.

Written by the indexing model from the issue text.