Cancel immediate read callback when socket has error

Summary:
When `startFail()` is called, it sets the state to StateEnum::ERROR.
There is a chance that immediate read callback is scheduled to run in
next event loop. The callback calls handleRead() then triggers
`assert(state_ == StateEnum::ESTABLISHED)` in `AsyncSokcet::handleRead`.

Cancel any immediate read callback when startFail is called.

Reviewed By: yfeldblum

Differential Revision: D7051956

fbshipit-source-id: 0d6693d851b272355a4f36ab8d001969fa47750e

folly/io/async/AsyncSocket.cpp

@@ -2473,6 +2473,11 @@ void AsyncSocket::startFail() {
   // so all future attempts to read or write will be rejected
   shutdownFlags_ |= (SHUT_READ | SHUT_WRITE);
 
+  // Cancel any scheduled immediate read.
+  if (immediateReadHandler_.isLoopCallbackScheduled()) {
+    immediateReadHandler_.cancelLoopCallback();
+  }
+
   if (eventFlags_ != EventHandler::NONE) {
     eventFlags_ = EventHandler::NONE;
     ioHandler_.unregisterHandler();