Fix slice index panic in add_rest_param

[0x7D2B]

This Pull Request fixes #1241.

[github-actions]

Test262 conformance changes:

Test result	master count	PR count	difference
Total	78,873	78,873	0
Passed	26,502	26,504	+2
Ignored	15,604	15,604	0
Failed	36,767	36,765	-2
Panics	27	24	-3
Conformance	33.60%	33.60%	+0.00%

[github-actions]

Benchmark for caf2a21

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Test	PR Benchmark	Master Benchmark	%
Arithmetic operations (Execution)	399.7±20.32ns	403.6±22.13ns	-0.97%
Arithmetic operations (Full)	315.8±12.05µs	317.2±13.27µs	-0.44%
Array access (Execution)	7.5±0.49µs	7.4±0.37µs	+1.35%
Array access (Full)	356.0±28.75µs	348.7±13.38µs	+2.09%
Array creation (Execution)	3.0±0.11ms	3.1±0.17ms	-3.23%
Array creation (Full)	3.4±0.22ms	3.3±0.10ms	+3.03%
Array pop (Execution)	975.6±31.20µs	987.1±27.48µs	-1.17%
Array pop (Full)	1509.7±51.25µs	1511.8±51.56µs	-0.14%
Boolean Object Access (Execution)	6.0±0.22µs	6.2±0.25µs	-3.23%
Boolean Object Access (Full)	336.8±12.84µs	336.9±13.66µs	-0.03%
Clean js (Execution)	729.5±27.14µs	754.9±43.45µs	-3.36%
Clean js (Full)	1078.1±49.93µs	1114.3±46.13µs	-3.25%
Clean js (Parser)	47.2±2.71µs	46.5±2.28µs	+1.51%
Create Realm	450.4±23.76ns	453.9±22.93ns	-0.77%
Dynamic Object Property Access (Execution)	6.2±0.31µs	6.1±0.38µs	+1.64%
Dynamic Object Property Access (Full)	340.3±13.04µs	352.0±25.15µs	-3.32%
Expression (Parser)	7.6±0.28µs	7.6±0.40µs	0.00%
Fibonacci (Execution)	938.9±29.55µs	938.3±44.47µs	+0.06%
Fibonacci (Full)	1313.6±50.62µs	1271.8±52.47µs	+3.29%
For loop (Execution)	25.2±0.95µs	25.5±1.28µs	-1.18%
For loop (Full)	363.4±13.96µs	359.5±11.65µs	+1.08%
For loop (Parser)	22.4±1.21µs	22.3±0.80µs	+0.45%
Goal Symbols (Parser)	15.7±0.74µs	15.8±4.11µs	-0.63%
Hello World (Parser)	4.4±0.16µs	4.3±0.26µs	+2.33%
Long file (Parser)	844.5±59.92ns	839.8±66.30ns	+0.56%
Mini js (Execution)	660.6±27.74µs	661.0±34.41µs	-0.06%
Mini js (Full)	1016.4±61.83µs	1033.2±46.35µs	-1.63%
Mini js (Parser)	39.8±1.06µs	40.9±2.24µs	-2.69%
Number Object Access (Execution)	4.8±0.21µs	4.7±0.32µs	+2.13%
Number Object Access (Full)	329.8±18.02µs	340.4±18.98µs	-3.11%
Object Creation (Execution)	5.3±0.25µs	5.3±0.29µs	0.00%
Object Creation (Full)	362.0±151.39µs	336.3±12.92µs	+7.64%
RegExp (Execution)	13.0±0.71µs	12.6±0.81µs	+3.17%
RegExp (Full)	358.2±16.73µs	360.0±14.50µs	-0.50%
RegExp Literal (Execution)	12.6±0.51µs	12.4±0.59µs	+1.61%
RegExp Literal (Full)	356.6±24.41µs	356.6±23.72µs	0.00%
RegExp Literal Creation (Execution)	10.9±0.40µs	11.0±0.54µs	-0.91%
RegExp Literal Creation (Full)	342.1±18.28µs	353.7±12.45µs	-3.28%
Static Object Property Access (Execution)	5.7±0.32µs	5.6±0.27µs	+1.79%
Static Object Property Access (Full)	338.8±23.66µs	346.5±21.75µs	-2.22%
String Object Access (Execution)	8.3±0.34µs	8.3±0.34µs	0.00%
String Object Access (Full)	339.1±12.06µs	347.3±11.41µs	-2.36%
String comparison (Execution)	7.5±0.30µs	7.6±0.33µs	-1.32%
String comparison (Full)	350.5±16.28µs	343.1±21.28µs	+2.16%
String concatenation (Execution)	6.1±0.25µs	6.1±0.23µs	0.00%
String concatenation (Full)	341.3±18.48µs	335.5±12.09µs	+1.73%
String copy (Execution)	4.7±0.20µs	4.6±0.16µs	+2.17%
String copy (Full)	323.4±10.00µs	329.1±10.20µs	-1.73%
Symbols (Execution)	4.0±0.22µs	4.0±0.31µs	0.00%
Symbols (Full)	320.2±15.04µs	317.9±13.88µs	+0.72%