Fix ZMQ Notification initialization and shutdown

Moves the call Initialize() from init.cpp to CreateWithArguments() and handles the
return value. Moves the call Shutdown() from init.cpp to destructor.
Changes Initialize() and Shutdown() to protected members.

src/init.cpp

@@ -208,7 +208,6 @@ void Shutdown()
 #if ENABLE_ZMQ
     if (pzmqNotificationInterface) {
         UnregisterValidationInterface(pzmqNotificationInterface);
-        pzmqNotificationInterface->Shutdown();
         delete pzmqNotificationInterface;
         pzmqNotificationInterface = NULL;
     }
@@ -1170,7 +1169,6 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
     pzmqNotificationInterface = CZMQNotificationInterface::CreateWithArguments(mapArgs);
 
     if (pzmqNotificationInterface) {
-        pzmqNotificationInterface->Initialize();
         RegisterValidationInterface(pzmqNotificationInterface);
     }
 #endif

src/zmq/zmqnotificationinterface.cpp

@@ -21,8 +21,7 @@ CZMQNotificationInterface::CZMQNotificationInterface() : pcontext(NULL)
 
 CZMQNotificationInterface::~CZMQNotificationInterface()
 {
-    // ensure Shutdown if Initialize is called
-    assert(!pcontext);
+    Shutdown();
 
     for (std::list<CZMQAbstractNotifier*>::iterator i=notifiers.begin(); i!=notifiers.end(); ++i)
     {
@@ -59,6 +58,12 @@ CZMQNotificationInterface* CZMQNotificationInterface::CreateWithArguments(const
     {
         notificationInterface = new CZMQNotificationInterface();
         notificationInterface->notifiers = notifiers;
+
+        if (!notificationInterface->Initialize())
+        {
+            delete notificationInterface;
+            notificationInterface = NULL;
+        }
     }
 
     return notificationInterface;
@@ -99,7 +104,7 @@ bool CZMQNotificationInterface::Initialize()
         return false;
     }
 
-    return false;
+    return true;
 }
 
 // Called during shutdown sequence

src/zmq/zmqnotificationinterface.h

@@ -18,10 +18,11 @@ public:
 
     static CZMQNotificationInterface* CreateWithArguments(const std::map<std::string, std::string> &args);
 
+protected:
     bool Initialize();
     void Shutdown();
 
-protected: // CValidationInterface
+    // CValidationInterface
     void SyncTransaction(const CTransaction &tx, const CBlock *pblock);
     void UpdatedBlockTip(const uint256 &newHashTip);