Blender Git Loki

Fix T72006: Clay brush with size pressure corrupts mesh

When size pressure is enabled, the radius may not be enough to sample
any vertices to calculate the area normal. This lead to a vector 0 plane
and a division by 0 when calculating the signed distance to the plane,
which produces a NaN that was being written to the vertex coordinates.

Reviewed By: brecht

Maniphest Tasks: T72006

Differential Revision: https://developer.blender.org/D6326