Blender Git Loki

RNA code cleanup: Fix wrong usages of `rna_idproperty_check()`.

This function is more expansive than the simpler `rna_ensure_property()`
one, and should only be used when IDProperty data is actually needed.

If one only needs to ensure it has a valid PropertyRNA pointer,
`rna_ensure_property()` is much more efficient.

Also add compiler warnings when results of those functions are unused,
this should never be the case.