This commit fixes two different issues actually:
* When view name is unknown/irrelevant, you should pass a NULL str pointer to
`RE_RenderLayerGetPass()`, not an empty string!
* `render_result_rescale()` would unconditionnaly free re->result (at the end),
even if it did not replaced it at all, leading to freed memory access later.
This is only a partial fix though, "CacheBuffer" (i.e. saving tiles in EXR files)
shall not be used in 3DView rendering, and yet it is here...
1e71270f77