58 string expressions cannot be used as indices

[numeredev]

SUMMARY

Implements necessary changes for #58

Reviewers: @numere-org/maintainers

IMPLEMENTATION

• Implementation: Added new error codes for missing operands (which was the root cause for the endless loop) and only inserted single index expressions into the stirng parser
• Implementation test: Executed erroneous code without problems and ran the string tests. All problems were resolved. Here's a simple code snippet to check, whether the problem has been resolved:

par{} = getfileinfo("<>/numere.exe");
c{} = {1:16};
partable(1, 1+num(par{})/2:) = par{{2:2:nlen}};

DOCUMENTATION

• [x] ChangesLog updated
• [x] Code changes commented
• Documentation articles:
  • [ ] corresponding documentation articles updated
  • [ ] new documentation articles created
  • [x] not needed
• Language files:
  • [x] corresponding language files updated
  • [ ] not needed

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TESTS BY REVIEWERS

• [x] Added to the automatic SW tests
• [x] Tested manually