Blender Git Loki

Cleanup/Fix RNA array length accessors returning non-zero values in invalid cases.

This was apparently done in two places only, with a very cryptic comment
(`/* for raw_access, untested */`), and... I cannot see how returning a
non-zero length value for an array that does not exist or is not
accessible at least, would be anything but an obvious source of issues.

Note that both commits adding those lines are from stone ages (2009):
rBcbc2c1886dee and rB50e3bb7f5f34.