Fix wrong consumers size: execute `callback` before executing `readerCreatedCallback_`. (#17325)
Fix wrong consumers size: execute `callback` before executing `readerCreatedCallback_`. (#17325)

Fixes #14848

### Motivation

We should execute `callback` before executing `readerCreatedCallback_`, otherwise, we may get the wrong consumers size. More see:

https://github.com/apache/pulsar/blob/e23d312c04da1d82d35f9e2faf8a446f8e8a4eeb/pulsar-client-cpp/lib/ReaderImpl.cc#L84-L92

https://github.com/apache/pulsar/blob/c48a3243287c7d775459b6437d9f4b24ed44cf4c/pulsar-client-cpp/lib/ClientImpl.cc#L250-L254

### Modifications

execute `callback` before executing `readerCreatedCallback_`
yahoo/pulsar,merlimat/pulsar,massakam/pulsar,merlimat/pulsar,merlimat/pulsar,merlimat/pulsar,merlimat/pulsar,massakam/pulsar,massakam/pulsar,merlimat/pulsar,yahoo/pulsar,massakam/pulsar,yahoo/pulsar,yahoo/pulsar,yahoo/pulsar,yahoo/pulsar,massakam/pulsar,massakam/pulsar