MATXS formatted tape for constant spectrum and production for NZ>1

[dlopezaldama]

There is a bug in matxsr.f90 that incorrectly formats the constant spectrum vector (spec) and production vector (prod) when the number of Bondarenko background cross sections (sigz) is greater than one (NZ > 1).
This issue was reported by Ivo Kodeli, who encountered it while processing Pu-239 from JENDL-5.
However, the bug is systematic and could affect any evaluation where NZ > 1 for the magnitudes spec and prod.

[dlopezaldama]

Maybe it can also solve the issue #336