Revert easly glfwPollEvents() call

Causes crash on Windows when minimizing the eye window,
since `window_size` is set to `(0,0)` during glfw event handling.

pupil_src/launchables/eye.py

@@ -801,7 +801,6 @@ def window_should_update():
                                 )
 
                     glViewport(0, 0, *camera_render_size)
-                    glfw.glfwPollEvents()
                     make_coord_system_pixel_based((f_height, f_width, 3), g_pool.flip)
                     # render the ROI
                     g_pool.u_r.draw(g_pool.gui.scale)
@@ -825,6 +824,7 @@ def window_should_update():
 
                     # update screen
                     glfw.glfwSwapBuffers(main_window)
+                glfw.glfwPollEvents()
 
         # END while running