Fixes from reviewer

Call base version from aboutToFinish(); add comment for
script-engine logic.

assignment-client/src/Agent.cpp

@@ -336,7 +336,7 @@ void Agent::scriptRequestFinished() {
         }
 
         setFinished(true);
-        emit finished();
+        ThreadedAssignment::aboutToFinish();
     }
 
     request->deleteLater();
@@ -499,7 +499,7 @@ void Agent::executeScript() {
     DependencyManager::destroy<RecordingScriptingInterface>();
 
     setFinished(true);
-    emit finished();
+    ThreadedAssignment::aboutToFinish();
 }
 
 QUuid Agent::getSessionUUID() const {
@@ -827,10 +827,12 @@ void Agent::processAgentAvatarAudio() {
 void Agent::aboutToFinish() {
     setIsAvatar(false);// will stop timers for sending identity packets
 
+    // If script engine not started yet then finish up, else will be done when
+    // script engine exits.
     if (_scriptEngine) {
         _scriptEngine->stop();
     } else {
-        emit finished();
+        ThreadedAssignment::aboutToFinish();
     }
 
     // our entity tree is going to go away so tell that to the EntityScriptingInterface

assignment-client/src/assets/AssetServer.cpp

@@ -342,7 +342,7 @@ void AssetServer::aboutToFinish() {
     while (_pendingBakes.size() > 0) {
         QCoreApplication::processEvents();
     }
-    emit finished();
+    ThreadedAssignment::aboutToFinish();
 }
 
 void AssetServer::run() {

assignment-client/src/audio/AudioMixer.cpp

@@ -109,7 +109,7 @@ AudioMixer::AudioMixer(ReceivedMessage& message) :
 
 void AudioMixer::aboutToFinish() {
     DependencyManager::destroy<PluginManager>();
-    emit finished();
+    ThreadedAssignment::aboutToFinish();
 }
 
 void AudioMixer::queueAudioPacket(QSharedPointer<ReceivedMessage> message, SharedNodePointer node) {

assignment-client/src/entities/EntityServer.cpp

@@ -72,8 +72,7 @@ void EntityServer::aboutToFinish() {
     DependencyManager::get<ResourceManager>()->cleanup();
 
     OctreeServer::aboutToFinish();
-
-    emit finished();
+    ThreadedAssignment::aboutToFinish();
 }
 
 void EntityServer::handleEntityPacket(QSharedPointer<ReceivedMessage> message, SharedNodePointer senderNode) {

assignment-client/src/scripts/EntityScriptServer.cpp

@@ -588,5 +588,5 @@ void EntityScriptServer::aboutToFinish() {
         _encoder = nullptr;
     }
 
-    emit finished();
+    ThreadedAssignment::aboutToFinish();
 }