Fixed req_app_link reference counting on cancellation.
Fixed req_app_link reference counting on cancellation.

Re-scheduled req_app_link structures should have use_count exactly equal
to the number of references from the application and port list.  However,
there's one extra usage decrement that occurs after the req_app_link is
created because the use_count is initialised as 1.

This patch removes all excess instances of the usage decrement that caused
preliminary req_app_link release and router process crash.

To reproduce the issue need to cause request rescheduling between 2 app
processes.

This issue was introduced in 61e9f23a566d.

nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit