Blender Git Loki

Fix T53229: "Sample Keyframes" errors with multiple pairs of keyframes selected

There were 2 issues here (first was the one reported):
1) Curve shape changes if multiple consecutive pairs of keyframes
are selected. The problem is that after the first pair is handled,
subsequent pairs get sampled on the basis of the modified curve.

2) With multiple separate "islands" selected, unselected points in between
would get ignored, causing the entire curve to get sampled.