Fix double-onEgressResumed call

Summary: If two body events are present and queued, when the first one resolves, it calls `resumeClientIngress`, which results in any queued calls happening inline. This then results in the same call to `resumeClientIngress`, since from the HTTPTunnelSink's perspective, it hasn't run `handlerEgressPaused_ = false;` yet so thinks it still needs to pause ingress

Differential Revision: D67065077

fbshipit-source-id: abf23c74c76b7dd3e55ce71c03a8222d567f4286

third-party/proxygen/src/proxygen/lib/http/sink/HTTPTunnelSink.cpp

@@ -169,8 +169,8 @@ void HTTPTunnelSink::writeSuccess() noexcept {
     // If we drop below the max outstanding writes, resume egress
     if (outstandingWrites_ < kMaxOutstandingWrites && handlerEgressPaused_ &&
         handler_) {
-      handler_->onEgressResumed();
       handlerEgressPaused_ = false;
+      handler_->onEgressResumed();
     }
     resetIdleTimeout();
   }