Blender Git Loki

Fix: BLI_getenv returns ascii not UTF8 on windows

BLI_getenv has always incorrectly returned ascii rather
than UTF-8. This change corrects this behaviour.

This resolves issues when the `BLENDER_USER_CONFIG`
environment variable contains a path with Unicode characters
on windows as reported in T74510 (but unlikely the root
cause for the issue at hand there)

Differential Revision: https://developer.blender.org/D9831

Reviewed by: brecht