Handling of errors - like unstable network - coming via SSL

[bligeti]

Possible fix for #85 The trigger of this problem can be network disconnections or similar errors coming via SSL.

In HTTPConnection::updateBuffer() closeConnection() is called when error is detected from SSL to clean up but the possibility of already cleaned up session is not handled in HTTPConnection::pendingBufferSize() and in HTTPConnection::loop().

Also in such case WSHandler::onClose() is not called therefore the recorded handlers (like in the websocket example) are not cleaned up.