Blender Git Loki

RNA: always allow fallback from defaultarray to defaultvalue.

The python getters for the array already allowed that, but not the
actual C RNA access functions. This is inconsistent, so implement
the fallback in all cases. Now if by default the property should
contain the same value in all positions, it is not necessary to
actually use an array.

Reviewers: campbellbarton

Differential Revision: https://developer.blender.org/D3940