[REVIEW-3-6] fix for fdo#46100, limit the degree of b-spline algorithm in charts

[Markus Mohrhard]

Hey

[1] fixes one of our hard hacks. IT just inserts a hard limit for the
b-spline polynomial degree which is responsible for the crash in this
document. This document uses a degree of 50 and a resolution of 20
which creates millions of interpolation points. Normally a degree of 3
to 8 is enough for every document.

BTW, we(I know this mean I) finally need to find the problem in the
B-spline interpolation that makes it more or less unusable. See the
test document and click into the chart to get into edit mode.

Regards,
Markus

[1] http://cgit.freedesktop.org/libreoffice/core/commit/?id=e1dee0aaacd8e30e2949053ebf351d76bad14ac3