fix align_camera_center in Viewer::init() for multiple cores (#1349)

* Iterate over viewer.core_list and viewer.data_list and align_camera_center per core with visible data.

include/igl/opengl/glfw/Viewer.cpp

@@ -1,4 +1,4 @@
-// This file is part of libigl, a simple c++ geometry processing library.
+// This file is part of libigl, a simple c++ geometry processing library. 
 //
 // Copyright (C) 2014 Daniele Panozzo <[email protected]>
 //
@@ -210,13 +210,18 @@ namespace glfw
     glfwGetWindowSize(window, &width_window, &height_window);
     highdpi = windowWidth/width_window;
     glfw_window_size(window,width_window,height_window);
-    //opengl.init();
-    for(int i=0;i<core_list.size(); i++)
-    {
-      core_list[i].align_camera_center(data().V,data().F);
-    }
     // Initialize IGL viewer
     init();
+    for(auto &core : this->core_list)
+    {
+      for(auto &data : this->data_list)
+      {
+        if(data.is_visible & core.id)
+        {
+          this->core(core.id).align_camera_center(data.V, data.F);
+        }
+      }
+    }
     return EXIT_SUCCESS;
   }