src: check for tsfn in conditional_variable wait

Fixes: #1150

PR-URL: #1168
Reviewed-By: Michael Dawson <midawson@redhat.com

Author: KevinEady

test/threadsafe_function/threadsafe_function_sum.cc

@@ -81,7 +81,7 @@ class DelayedTSFNTask {
   // Entry point for std::thread
   void entryDelayedTSFN(int threadId) {
     std::unique_lock<std::mutex> lk(mtx);
-    cv.wait(lk);
+    cv.wait(lk, [this] { return this->tsfn != nullptr; });
     tsfn.BlockingCall([=](Napi::Env env, Function callback) {
       callback.Call({Number::New(env, static_cast<double>(threadId))});
     });

test/typed_threadsafe_function/typed_threadsafe_function_sum.cc

@@ -99,7 +99,7 @@ class DelayedTSFNTask {
   // Entry point for std::thread
   void entryDelayedTSFN(int threadId) {
     std::unique_lock<std::mutex> lk(mtx);
-    cv.wait(lk);
+    cv.wait(lk, [this] { return this->tsfn != nullptr; });
     tsfn.BlockingCall(new double(threadId));
     tsfn.Release();
   };