Bug Description:
If a connection enters in turbo mode (because of high traffic) or
a worker reads several requests in the read buffer (more_data), the thread
keeps processing connection.
In that condition it should not decrease the refcnt.
In case the operation is a persistent search, it decreases systematically
the refcnt.
So refcnt can become lower than the actual number of threads active on the connection.

Most of the time it can create messages like
    Attempt to release connection that is not acquired
In some rare case, if the a connection is out of the active list but a remaining thread
tries to remove it again it can lead to a crash

Fix Description:
The fix consist, when processing a PS, to decrease the refcnt at the condition
the connection is not in turbo mode or in more_data.

https://pagure.io/389-ds-base/issue/49768

Reviewed by: ?

Platforms tested: F26

Flag Day: no

Doc impact: no