Fix indexToPosition when index == -1

The -1 index is used throughout ImgLib2 to signify a position one step before the starting position. However, the indexToPosition calculations in IntervalIndexer were not taking the -1 index into account, producing incorrect position arrays for this index.

This patch fixes the indexToPosition calculations. To avoid copying and pasting the fix throughout all signatures, the array-based methods were refactored to funnel through a single method using SciJava-Common PrimitiveArrays.