Avoid writing to unallocated memory in quadratic cells.

The Contour method of quadratic cells needs to interpolate
extra points that are not defined in the data structure. Instead
of calling SetPoint and hoping that extra memory has been
allocated, use InsertPoint to ensure that the array will be
extended as needed.

Change-Id: I5c5d7efb1af16116c538ebbe718650d350388aa9
Merge topic 'quadratic-cells-memory' into master

25c5737c Avoid writing to unallocated memory in quadratic cells.