Guard some IdGroup calls by ID_AVAILABLE

[fingolfin]

... instead of hardcoding assumptions about the availability of IdGroup.

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 78.63%. Comparing base (b04e9ba) to head (ee87ece).

Files with missing lines	Patch %	Lines
lib/grplatt.gi	80.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6353   +/-   ##
=======================================
  Coverage   78.63%   78.63%           
=======================================
  Files         684      684           
  Lines      292689   292688    -1     
  Branches     8686     8660   -26     
=======================================
+ Hits       230153   230154    +1     
  Misses      60726    60726           
+ Partials     1810     1808    -2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[ThomasBreuer]

The old code uses IdGroup only if the group in question has order at most 1000. The proposed code uses it also for larger groups, for example for groups of order p^4, where p is any prime. Is this intended?

[ThomasBreuer]

This is irritating:
We have hom, and here we create its image, but a few lines above we create this group as gp/nor on the fly, just in order to call IdGroup.

[fingolfin]

Yeah that's weird. I've rearranged the code now to avoid this.

[fingolfin]

The limit to 1000 seemed arbitrary, perhaps an attempt approximate ID_AVAILABLE, so I left it out. But perhaps there is a deeper reason? Anyway, I'd be happy to add it back, though ideally with a comment explaining the limit...

The code was added by @hulpke on 2013-01-25, in a commit with commit message SubgroupsTrivialFitting. Perhaps he can tell us more?