When using the color picker on a image editor it tries to read the color
from the original image. When there is no original image the code
crashes during the determination of the UDIM tile number.
There are 2 approaches to solve this.
1. Modify `BKE_image_get_tile_from_pos` to support NULL pointers.
2. Modify `ED_space_image_color_sample` with an early exit.
This patch modifies `ED_space_image_color_sample` with an early exit.
Reviewed By: brecht
Differential Revision: https://developer.blender.org/D6629
42360e64da