fix(comb)!: Be consistent in asserting on programmer error

[epage]

This supersedes #368

[coveralls]

Pull Request Test Coverage Report for Build 7794016869

• -19 of 22 (13.64%) changed or added relevant lines in 3 files are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.2%) to 42.541%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/token/mod.rs	0	6	0.0%
src/combinator/multi.rs	2	15	13.33%
<!--	Total:	3	22	13.64%	-->

Files with Coverage Reduction	New Missed Lines	%
src/token/mod.rs	1	72.68%
src/ascii/mod.rs	2	54.68%
<!--	Total:	3		-->

Totals
Change from base Build 7763110062:	-0.2%
Covered Lines:	1306
Relevant Lines:	3070

---

💛 - Coveralls

[codecov[bot]]

Codecov Report

Attention: 19 lines in your changes are missing coverage. Please review.

Comparison is base (73e5c72) 42.74% compared to head (1b3480e) 42.54%.

Files	Patch %	Lines
src/combinator/multi.rs	13.33%	13 Missing :warning:
src/token/mod.rs	0.00%	6 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #449 +/- ## ========================================== - Coverage 42.74% 42.54% -0.21% ========================================== Files 18 18 Lines 3055 3070 +15 ========================================== Hits 1306 1306 - Misses 1749 1764 +15 ```

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