Don't access evb_ in AtomicNotificationQueue::size()

Summary:
evb_ can be updated by start/stopConsuming, so it's not safe to access it in the assertion (given that size() is thread safe).

(Note: this ignores all push blocking failures!)

Differential Revision: D24559287

fbshipit-source-id: b5886ce13fa54fb59361c1de110ec8bb02a06a12

folly/io/async/AtomicNotificationQueue.cpp

@@ -225,7 +225,6 @@ void AtomicNotificationQueue::setMaxReadAtOnce(uint32_t maxAtOnce) {
 int32_t AtomicNotificationQueue::size() const {
   auto queueSize = atomicQueue_.getPushCount() -
       taskExecuteCount_.load(std::memory_order_relaxed);
-  DCHECK(!evb_ || !evb_->isInEventBaseThread() || queueSize >= 0);
   return queueSize >= 0 ? queueSize : 0;
 }