Fixes an error with the handled flag for certificate exchange

Summary:
This change fixes a bug with the handled flag during the certificate exchange process.

Explanation:
handled was passed by reference as &handled
Once the function goes out of scope then the reference, well, it just becomes invalid (undefined behaviour)
In some cases, it appears as 'handled' because the reference is invalid and it happens to be 'true'.

Changelog: Fixed an issue where clients would randomly not connect to Flipper. Please update FlipperKit to 0.110.0 to apply the fix: https://fbflipper.com/docs/getting-started/react-native#using-the-latest-flipper-sdk

Reviewed By: mweststrate

Differential Revision: D31017592

fbshipit-source-id: c087a769fa23de1acfd3c198b4db4d6ccdb2be90

xplat/Flipper/FlipperConnectionManagerImpl.cpp

@@ -366,12 +366,13 @@ void FlipperConnectionManagerImpl::requestSignedCertFromFlipper() {
       "destination",
       contextStore_->getCertificateDirectoryPath().c_str())("medium", medium);
   auto gettingCert = flipperState_->start("Getting cert from desktop");
-  bool handled = false;
 
-  flipperEventBase_->add([this, &handled, message, gettingCert]() {
+  certificateExchangeCompleted_ = false;
+
+  flipperEventBase_->add([this, message, gettingCert]() {
     client_->sendExpectResponse(
         folly::toJson(message),
-        [this, &handled, message, gettingCert](
+        [this, message, gettingCert](
             const std::string& response, bool isError) {
           /**
             Need to keep track of whether the response has been handled.
@@ -382,9 +383,9 @@ void FlipperConnectionManagerImpl::requestSignedCertFromFlipper() {
             interrupted because we are effectively still handing the response
             read. So, if already handled, ignore and return;
           */
-          if (handled)
+          if (certificateExchangeCompleted_)
             return;
-          handled = true;
+          certificateExchangeCompleted_ = true;
           if (isError) {
             if (response.compare("not implemented")) {
               auto error =