BUG: Check VTK Renderer exists on resetCamera

Was crashing when starting the simulation without interacting first

Base/SimulationManager/imstkInteractorStyle.cpp

@@ -50,8 +50,13 @@ InteractorStyle::OnTimer()
     // Update render delegates
     m_simManager->getViewer()->getCurrentRenderer()->updateRenderDelegates();
 
+    // Reset camera clipping range
+    if(this->CurrentRenderer != nullptr)
+    {
+        this->CurrentRenderer->ResetCameraClippingRange();
+    }
+
     // Render
-    this->CurrentRenderer->ResetCameraClippingRange();
     this->Interactor->Render();
 }