Fixes for Mac build and crash on startup

For some reason the qt code gen is getting confused by the #if 0
in 3DConnextionClient.h, so I added a stub implementation.

In Application.cpp the change of moving idle into paintGL had a sideeffect
of calling OffscreenGlCanvas before it was initialized.  To work around this
I added a guard to prevent calling idle before all the gl windows/widgets have
been initialized.

interface/src/Application.cpp

@@ -940,14 +940,12 @@ void Application::initializeGL() {
     qCDebug(interfaceapp) << "Created Display Window.";
 
     // initialize glut for shape drawing; Qt apparently initializes it on OS X
-    #ifndef __APPLE__
-    static bool isInitialized = false;
-    if (isInitialized) {
+    if (_isGLInitialized) {
         return;
     } else {
-        isInitialized = true;
+        _isGLInitialized = true;
     }
-    #endif
+
     // Where the gpuContext is initialized and where the TRUE Backend is created and assigned
     gpu::Context::init<gpu::GLBackend>();
     _gpuContext = std::make_shared<gpu::Context>();
@@ -1059,7 +1057,9 @@ void Application::paintGL() {
         _lastFramesPerSecondUpdate = now;
     }
 
-    idle(now);
+    if (_isGLInitialized) {
+        idle(now);
+    }
 
     PROFILE_RANGE(__FUNCTION__);
     PerformanceTimer perfTimer("paintGL");

interface/src/Application.h

@@ -414,7 +414,7 @@ private:
 
     bool _dependencyManagerIsSetup;
 
-    OffscreenGlCanvas* _offscreenContext;
+    OffscreenGlCanvas* _offscreenContext {nullptr};
     DisplayPluginPointer _displayPlugin;
     InputPluginList _activeInputPlugins;
 
@@ -548,6 +548,7 @@ private:
     quint64 _lastSimsPerSecondUpdate = 0;
     bool _isForeground = true; // starts out assumed to be in foreground
     bool _inPaint = false;
+    bool _isGLInitialized {false};
 };
 
 #endif // hifi_Application_h

interface/src/devices/3DConnexionClient.h

@@ -220,4 +220,19 @@ public:
 
 #endif
 
+#include <QObject>
+#include <QLibrary>
+
+// stub
+class ConnexionClient : public QObject {
+    Q_OBJECT
+public:
+    static ConnexionClient& getInstance();
+    void init() {};
+    void destroy() {};
+    bool Is3dmouseAttached() { return false; };
+public slots:
+    void toggleConnexion(bool shouldEnable) {};
+};
+
 #endif // defined(hifi_3DConnexionClient_h)