Fix T80395: Cycles baking crash when Surfaces are disabled in the view layer

Always enable surfaces for baking, otherwise there is nothing to bake to.

Differential Revision: https://developer.blender.org/D9015

Fix T80859: Thread safe pixeldata concersion from float to uchar and v.v.

I created a bugreport T80859 earlier.

The problem is in the file source/blender/editors/sculpt_paint/paint_image_proj.c (line numbers against commit d376aea61)

at the lines 5309 and 5320 the functions `IMB_rect_from_float(...)` and `IMB_float_from_rect(...)` are called from threaded code on a shared ibuf.
However, ps->reproject_ibuf is shared between threads, so this is not thread-safe.
This is a race condition and leads to wrong output when projecting float data onto a uchar texture or vice versa on a multithreaded system.
The checks on line 5308 and 5319 are already a race condition.

I created this patch which fixes the problem , but I'm not sure if I'm overlooking something.
This makes sure reproject_ibuf contains the correct formats *before* the threadpool is started.

I replaced the original location of the conversions with BLI_asserts(). That may be overkill?

Reviewed By: #sculpt_paint_texture, mont29

Maniphest Tasks: T80859

Differential Revision: https://developer.blender.org/D8936