2741: Fix PD parameter issue

[krzywon]

Description

A change to the PD params resulted in width, npts, and nsigmas to all change width of the underlying model. This corrects that behavior.

Fixes #2741

Review Checklist:

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Documentation (check at least one)

• There is nothing that needs documenting
• Documentation changes are in this PR
• There is an issue open for the documentation (link?)

Installers

• There is a chance this will affect the installers, if so
  • Windows installer (GH artifact) has been tested (installed and worked)
  • MacOSX installer (GH artifact) has been tested (installed and worked)

Licencing (untick if necessary)

• The introduced changes comply with SasView license (BSD 3-Clause)

[rozyczko]

I was unable to reproduce the issue, so can't say this fixes the problem, but the code looks OK.