Fix crash when at-function-named-arguments encounters trailing commas in function calls

[thibaudcolas]

When at-function-named-arguments is enabled, stylelint crashes when the rule attempts to parse function calls that have a trailing comma (has been part of Sass since ± 2016). For example:

.b {
  border: reset(
    $value: 40px,
  );
}

This will cause the following error:

    TypeError: Cannot read property 'key' of undefined

       98 |             case "always": {
    >  99 |               if (arg.key && isScssVarRegExp.test(arg.key)) {
          |                                                    ^
      100 |                 return;
      101 |               }

      at src/rules/at-function-named-arguments/index.js:99:52
      [...]

---

The error is caused by groupByKeyValue of parseFunctionArguments, which creates an empty group when seeing the comma. It seems like a simple fix would be to ignore the comma if it is trailing, this seems to work based on the tests I added.

[coveralls]

Coverage increased (+0.02%) to 92.287% when pulling 7be866f on thibaudcolas:bug/at-function-named-arguments-trailing-comma into 993f32e on kristerkari:master.

[kristerkari]

Thanks! The fix looks good.

[kristerkari]

the fix is available in version 3.3.1 👍

[thibaudcolas]

Thank you 👌 I can confirm it works on my project!