fix random crash on interface shutdown

interface/src/VoxelHideShowThread.cpp

@@ -18,6 +18,7 @@
 
 VoxelHideShowThread::VoxelHideShowThread(VoxelSystem* theSystem) :
     _theSystem(theSystem) {
+    //qDebug() << "VoxelHideShowThread::VoxelHideShowThread() this=" << this;
 }
 
 bool VoxelHideShowThread::process() {

libraries/octree/src/JurisdictionListener.cpp

@@ -18,6 +18,9 @@
 JurisdictionListener::JurisdictionListener(NODE_TYPE type, PacketSenderNotify* notify) : 
     _packetSender(notify, JurisdictionListener::DEFAULT_PACKETS_PER_SECOND)
 {
+    //qDebug() << "JurisdictionListener::JurisdictionListener() this=" << this;
+    //qDebug() << "JurisdictionListener::JurisdictionListener() this=" << this << " _packetSender=" << &_packetSender;
+
     _nodeType = type;
     ReceivedPacketProcessor::_dontSleep = true; // we handle sleeping so this class doesn't need to
     

libraries/octree/src/OctreePersistThread.cpp

@@ -20,6 +20,7 @@ OctreePersistThread::OctreePersistThread(Octree* tree, const QString& filename,
     _persistInterval(persistInterval),
     _initialLoadComplete(false),
     _loadTimeUSecs(0) {
+    //qDebug() << "OctreePersistThread::OctreePersistThread()... this=" << this;
 }
 
 bool OctreePersistThread::process() {

libraries/shared/src/GenericThread.cpp

@@ -17,10 +17,16 @@ GenericThread::GenericThread() :
     _stopThread(false),
     _isThreaded(false) // assume non-threaded, must call initialize()
 {
+    //qDebug() << "GenericThread::GenericThread() this=" << this;
 }
 
 GenericThread::~GenericThread() {
-    terminate();
+    //qDebug() << "GenericThread::~GenericThread() this=" << this;
+    
+    // we only need to call terminate() if we're actually threaded and still running
+    if (isStillRunning() && isThreaded()) {
+        terminate();
+    }
 }
 
 void GenericThread::initialize(bool isThreaded) {
@@ -39,12 +45,14 @@ void GenericThread::initialize(bool isThreaded) {
 }
 
 void GenericThread::terminate() {
+    //qDebug() << "GenericThread::terminate()... this=" << this;
     if (_isThreaded) {
         _stopThread = true;
 
         if (_thread) {
             _thread->wait();
             _thread->deleteLater();
+            _thread = NULL;
         }
     }
 }
@@ -66,6 +74,7 @@ void GenericThread::threadRoutine() {
 
     // If we were on a thread, then quit our thread
     if (_isThreaded && _thread) {
+        //qDebug() << "GenericThread::threadRoutine()... about to call _thread->quit() this=" << this << " _thread=" << _thread;
         _thread->quit();
     }
 

libraries/shared/src/PacketSender.cpp

@@ -42,6 +42,7 @@ PacketSender::PacketSender(PacketSenderNotify* notify, int packetsPerSecond) :
     _totalPacketsQueued(0),
     _totalBytesQueued(0)
 {
+    //qDebug() << "PacketSender::PacketSender()... this=" << this;
 }
 
 PacketSender::~PacketSender() {

libraries/shared/src/ReceivedPacketProcessor.cpp

@@ -14,6 +14,7 @@
 
 ReceivedPacketProcessor::ReceivedPacketProcessor() {
     _dontSleep = false;
+    //qDebug() << "ReceivedPacketProcessor::ReceivedPacketProcessor()... this=" << this;
 }
 
 void ReceivedPacketProcessor::queueReceivedPacket(const HifiSockAddr& address, unsigned char* packetData, ssize_t packetLength) {