BUG: Fix nodata handling in StreamingStatisticsMapFromLabelImageFilter

Summary

StreamingStatisticsMapFromLabelImageFilter doesn't handle no data values properly.

Rationale

Fixes #2019

Implementation Details

We produce the no data value for min and max when no valid pixels were found.

Additional notes

I'm not really a fan of the current accumulator structure that's used in this and related filters. It has two operations:

• add a pixel
• merge two accumulators

I would prefer having:

• make a "zero" accumulator
• merge two accumulators

But that's another story.

Copyright

The copyright owner is Laurențiu Nicola (CS ROMANIA) and has signed the ORFEO ToolBox Contributor License Agreement.

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