Time animation screenshot fixes

This MR fixes two issues currently present with time animations.

• The scene view might not be in the correct context while rendering the time animation step, resulting in a black screenshot result.
• The time animation might save a wrong image at the beginning if the time animation delay is set too short. Instead, the scene view now makes the screenshot after rendering the scene, instead of when the screenshot wants to be taken.

The second issue should improve usability, because the user should no longer be required to set the delay to something large, to ensure the scene is rendered before taking the image.