Empty set leads to segfault on codes

Perhaps easy to fix:

On codes;
Set empty;
.end

FORM 5.0.0-beta.1 (Feb 27 2024, v5.0.0-beta.1-25-gb1f9041)  Run: Mon Mar  4 18:09:15 2024
...
 Sets
   pos_(0): integers > 0
   pos0_(1): integers >= 0
   neg_(2): integers < 0
   neg0_(3): integers <= 0
   even_(4): even integers
   odd_(5): odd integers
   int_(6): all integers
   symbol_(7): only symbols
   fixed_(8): fixed indices
   index_(9): all indices
   number_(10): all rationals
   dummyindices_(11): dummy indices
   vector_(12): only vectors
==34361== Invalid read of size 4
==34361==    at 0x208672: WriteLists (sch.c:1047)
==34361==    by 0x1522A8: DoExecute (execute.c:789)
==34361==    by 0x182388: ExecModule (module.c:291)
==34361==    by 0x1DD5D6: PreProcessor (pre.c:1041)
==34361==    by 0x21ADD9: main (startup.c:1688)
==34361==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==34361==
Program terminating at test.frm Line 2 -->

vermaseren / form

Empty set leads to segfault on codes #486