Use-after-free bug

[maryryang]

The following code flow produces a use-after-free bug:

1. We call zoo_awexists here: https://github.com/flightaware/zookeepertcl/blob/master/generic/zookeepertcl.c#L1270
2. The full initialization fails here: https://github.com/apache/zookeeper/blob/master/zookeeper-client/zookeeper-client-c/src/zookeeper.c#L3796. This means that we did still register the callback here: https://github.com/apache/zookeeper/blob/master/zookeeper-client/zookeeper-client-c/src/zookeeper.c#L3793. And we will still queue the zookeeper request here: https://github.com/apache/zookeeper/blob/master/zookeeper-client/zookeeper-client-c/src/zookeeper.c#L3806. AND zoo_awexists will return a ZMARSHALLINGERROR.
3. Since we return the ZMARSHALLINGERROR, we call free here: https://github.com/flightaware/zookeepertcl/blob/master/generic/zookeepertcl.c#L1273, but we are STILL going to receive a callback from zookeeper.
4. When we receive the callback (https://github.com/flightaware/zookeepertcl/blob/master/generic/zookeepertcl.c#L489), we are using the same zsc pointer that we have already freed.

[resuna]

Still getting a use-after-free problem with this change. Going to change the semantics of the synchronous calls to use the synchronous zookeeper API to resolve this and some other bugs, if you need to keep the event loop running while you're doing a pseudo-synchronous zookeeper operation you will have to explicitly do things with the -async callback option and vwait.

This will be either v1.1.0 or v2.0.0.

[resuna]

Fixed in v1.1.0