Blender Git Loki

T90908: Reduce loading times when extracting thumbnails from Blendfiles.

Previously when loading an thumbnails for an asset the whole file was
read. Reason this was done was perhaps a future idea to load
all thumbnails inside a blendfile in a single go. This was never implemented
and currently unneeded disk and cpu cycles was spend with finding out what
preview to load.

This patch adds an early break when the thumbnail that the caller is
interested in has been found. This improves the thumbnail extraction
when looking into large files.

Reviewed By: mont29

Maniphest Tasks: T90908

Differential Revision: https://developer.blender.org/D12312