Exceptions not handled properly in the proxy's AsyncTunnelHTTPConnection leading to the leaks and pool starvation

[janosik47]

The problem is described in #921

I made a proposal how to fix it in a comment

[rail-chamidullin-myriad]

@janosik47 I am dealing exactly with the same issue and I got to the same conclusion as you. Any update on this? Is there some PR with the fix?