Blender Git Loki

Fix T82703: Image not scaled when rendering

This is was caused by incorrectly set preview_render_size in VSE
rendering context. Value was set to SEQ_PROXY_RENDER_SIZE_FULL, but
it should be SEQ_PROXY_RENDER_SIZE_SCENE as scene render size is
being used.

This is same fix as 0d7036b40e68, but I did not checked openGL
render pipeline.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D9562