Blender Git Loki

Fix T73233: Image Editor Color Picker Crash

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