fix(noUnusedVariables): don't panic when renaming ref at the start

[Conaclos]

Summary

Fix #4114

Test Plan

I added a test.

[github-actions]

Parser conformance results on

js/262

Test result	main count	This PR count	Difference
Total	48517	48517	0
Passed	47326	47326	0
Failed	1191	1191	0
Panics	0	0	0
Coverage	97.55%	97.55%	0.00%

jsx/babel

Test result	main count	This PR count	Difference
Total	40	40	0
Passed	37	37	0
Failed	3	3	0
Panics	0	0	0
Coverage	92.50%	92.50%	0.00%

symbols/microsoft

Test result	main count	This PR count	Difference
Total	6571	6571	0
Passed	2203	2203	0
Failed	4368	4368	0
Panics	0	0	0
Coverage	33.53%	33.53%	0.00%

ts/babel

Test result	main count	This PR count	Difference
Total	680	680	0
Passed	608	608	0
Failed	72	72	0
Panics	0	0	0
Coverage	89.41%	89.41%	0.00%

ts/microsoft

Test result	main count	This PR count	Difference
Total	18471	18471	0
Passed	14144	14144	0
Failed	4327	4327	0
Panics	0	0	0
Coverage	76.57%	76.57%	0.00%

[arendjr]

Why use checked_add() if you're just going to unwrap() anyway?

Suggested change

	start.checked_add(1.into()).unwrap(),
	start + 1.into(),