3016: Fix to PD changes

[krzywon]

Description

This takes the fix applied in #2991 a step further. The original fix did not account for the error column, and continued to modified the .width param regardless of the value changed.

Fixes #3016

How Has This Been Tested?

Tested locally - different function produce different shape distributions.

Review Checklist:

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)

[butlerpd]

Looks reasonable and behaves as expected now.

I don't think it is new to this PR? But I noticed that the first change of polydisperse function on a given parameter triggers a run of the calculation but not for any future changes of function. I would think it is either a calculation whenever the function changes or never?