Loop counter variable used twice

[simonpierredeschenes]

The variable i is used as a counter in both the outer and inner loops.

https://github.com/ethz-asl/libpointmatcher/blob/c0d13ea87d3f6ccb81cbf0f9dc02a118a0c42f03/pointmatcher/DataPointsFilters/SurfaceNormal.cpp#L205