No data management

Since the introduction of thermal noise removal, some input low value can be set to zero (some pixel can have an input value inferior to the thermal noise) in the output product. This zero value is used to managed negative value according to the Eq.1 of the IPF document which have been used in OTB code.

The assumption used to manage the border mask is no more valid (pixels equal to 0 in output are no data).

Scene concatenation can be affected by this 0 values.

Moreover use 0 value which is a valid value as no data is confusing for end users.