Followup fix to #2177 with correct order of memset args

[tkittel]

Free-form text area

This one-liner is a fix to incorrect memset ordering args introduced in #2177. I had not noticed, since McStas warnings are not errors, and all CI ran green, but fortunately @mads-bertelsen spotted a compilation warning.

Why did it run green? Most likely the incorrect memset call had no effect (size parameter was inadvertently 0), so the struct was just as uninitialized as before #2177.

Suggestions for how we can perhaps try to make sure the CI catches this in the future:

1. It would be awesome if we could slowly one by one work on turning warnings into errors.
2. Run CI where malloc does not return zero initialised memory. I believe we could achieve this by setting (at least on ubuntu) MALLOC_PERTURB_=123 (or even MALLOC_PERTURB_=$(($RANDOM % 255 + 1))).

@willend let me know if you wish me to turn any of the above suggestions into an issue.

---

Development OS / boundary conditions

Please describe what OS you developed and tested your additions on, and if any special dependencies are required:

---

PR Checklist for contributing to McStas/McXtrace

For a coherent and useful contribution to McStas/McXtrace, please fill in relevant parts of the checklist:

• My contribution includes patches to an existing component file

  • I have used the mcdoc utility and rendered a reasonable documentation page for the component (please attach as screenshot in comments!)
  • I have ensured that basic use of the component is OK (e.g. an instrument using it compiles?)
  • I have used the mctest utility to test one or more instruments making use of the component (please attach mcviewtest report as screenshot in comments)
  • I have used the mcrun --c-lint "linter" and followed advice to remove most / all warnings that are raised

• My contribution includes patches to an existing instrument file

  • I have used the mcdoc utility and rendered a reasonable documentation page for the instrument (please attach as screenshot in comments!)
  • I have used the mctest utility to test the instrument (please attach mcviewtest report as screenshot in comments)
  • I have used the mcrun --c-lint "linter" and followed advice to remove most / all warnings that are raised

• My contribution includes a new component file

  • I have ensured that naming of parameters are in the style of existing components. (Please check the McStas or McXtrace NOMENCLATURE docs.)
  • I have ensured that component parameters are in the usually units of McStas or McXtrace (SI + neutron/x-ray 'usual' units)
  • I have used the mcdoc utility and rendered a reasonable documentation page for the component (please attach as screenshot in comments!)
  • I have ensured that basic use of the component is OK (e.g. an instrument using it compiles?)
  • I have included a corresponding example instrument and will fill in the new instrument section below
  • My new component is added within the contrib component category

• My contribution includes a new instrument file

  • I have used the mcdoc utility and rendered a reasonable documentation page for the instrument (please attach as screenshot in comments!)
  • I have ensured that basic use of the instrument is OK (e.g. it compiles?)
  • ... and provided reasonable default parameters in that instrument that produce reasonable output
  • ... and maybe even added a %Example: line to describe expected behaviour
  • I have used the mcrun --c-lint "linter" and followed advice to remove most / all warnings that are raised
  • My new instrument is added within the examples hierarchy in a folder in the style of examples/ESS/New_stuff/New_stuff.instr
  • My new instrument has a new, unique filename, not clashing with existing example instruments
  • My new instrument requires a data/input file. If the datafile is specific for my instrument I have left it in the same example folder, but if general use I have placed it in the global data folder.

• My work touches the code-generator in mccode/src

  • I have added reasoning and documentation for the change through an ADR record in our GRAMMAR section
  • I am attaching test output in the comments

• My work touches / adds to the runtime lib code (.c,.h etc in multiple locations

  • I am have added reasoning and documentation for the change below
  • I am attaching test output in the comments

• My PR is meant to fix a specific, existing issue

  • I have indicated the issue number here:
  • I have added documentation for the fix and possible side effects

• My contribution contains something else

  • Explanation is added in free form text above or below the checklist

---

[willend]

@tkittel thanks for this - seems a healthy patch as well as good suggestions for issues / further improvement! Please do formulate issues along these lines!

Merging.