Fixed String.prototype.indexOf() bug, when the search string is empty

[HalidOdat]

It changes the following:

• Fixed String.prototype.indexOf() bug, when the search string is empty
• Added test.

[codecov]

Codecov Report

Merging #599 into master will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #599      +/-   ##
==========================================
+ Coverage   71.23%   71.26%   +0.02%     
==========================================
  Files         177      177              
  Lines       11588    11598      +10     
==========================================
+ Hits         8255     8265      +10     
  Misses       3333     3333              

Impacted Files	Coverage Δ
boa/src/builtins/string/mod.rs	46.86% <100.00%> (+0.29%)	⬆️
boa/src/builtins/string/tests.rs	100.00% <100.00%> (ø)

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[github-actions]

Benchmark for 65771d2

Click to view benchmark

Test	PR Benchmark	Master Benchmark	%
Arithmetic operations (Execution)	365.1±13.54ns	388.7±12.54ns	-6.07%
Arithmetic operations (Full)	188.7±10.34µs	188.3±9.44µs	+0.21%
Array access (Execution)	9.3±0.34µs	9.5±0.41µs	-2.11%
Array access (Full)	205.3±5.66µs	210.6±7.48µs	-2.52%
Array creation (Execution)	3.2±0.10ms	3.4±0.09ms	-5.88%
Array creation (Full)	3.7±0.14ms	3.6±0.09ms	+2.78%
Array pop (Execution)	1182.4±49.37µs	1229.6±153.51µs	-3.84%
Array pop (Full)	1521.7±54.51µs	1532.4±43.61µs	-0.70%
Boolean Object Access (Execution)	4.9±0.21µs	5.0±0.19µs	-2.00%
Boolean Object Access (Full)	204.4±13.19µs	197.4±7.50µs	+3.55%
Create Realm	459.6±109.84ns	449.2±16.03ns	+2.32%
Dynamic Object Property Access (Execution)	5.9±0.22µs	5.8±0.46µs	+1.72%
Dynamic Object Property Access (Full)	207.9±14.20µs	204.6±7.57µs	+1.61%
Expression (Lexer)	2.5±0.17µs	2.5±0.09µs	0.00%
Expression (Parser)	5.3±0.17µs	5.3±0.17µs	0.00%
Fibonacci (Execution)	1076.9±52.50µs	1082.4±60.13µs	-0.51%
Fibonacci (Full)	1320.5±58.39µs	1324.7±66.98µs	-0.32%
For loop (Execution)	24.4±1.90µs	23.4±0.87µs	+4.27%
For loop (Full)	217.4±13.56µs	224.4±11.80µs	-3.12%
For loop (Lexer)	5.4±0.21µs	5.5±0.31µs	-1.82%
For loop (Parser)	15.1±0.64µs	14.9±1.05µs	+1.34%
Goal Symbols (Parser)	8.6±0.40µs	9.3±0.80µs	-7.53%
Hello World (Lexer)	868.8±45.82ns	880.7±44.85ns	-1.35%
Hello World (Parser)	2.2±0.08µs	2.2±0.11µs	0.00%
Long file (Parser)	6.7±0.22ms	6.8±0.27ms	-1.47%
Number Object Access (Execution)	3.8±0.25µs	3.9±0.19µs	-2.56%
Number Object Access (Full)	196.2±7.57µs	196.6±5.64µs	-0.20%
Object Creation (Execution)	5.0±0.14µs	5.0±0.22µs	0.00%
Object Creation (Full)	225.0±7.05µs	231.9±7.64µs	-2.98%
RegExp (Execution)	76.3±2.53µs	77.5±3.17µs	-1.55%
RegExp (Full)	314.3±13.37µs	326.7±11.81µs	-3.80%
RegExp Literal (Execution)	76.8±3.86µs	77.5±2.66µs	-0.90%
RegExp Literal (Full)	281.4±9.24µs	294.4±13.30µs	-4.42%
RegExp Literal Creation (Execution)	73.2±2.17µs	75.8±13.76µs	-3.43%
RegExp Literal Creation (Full)	324.0±14.42µs	318.9±14.15µs	+1.60%
Static Object Property Access (Execution)	5.3±0.16µs	5.2±0.27µs	+1.92%
Static Object Property Access (Full)	205.3±11.32µs	202.2±6.61µs	+1.53%
String Object Access (Execution)	6.9±0.35µs	7.4±0.38µs	-6.76%
String Object Access (Full)	200.8±6.99µs	205.1±17.60µs	-2.10%
String comparison (Execution)	7.1±0.33µs	7.2±0.32µs	-1.39%
String comparison (Full)	195.7±18.94µs	203.7±13.16µs	-3.93%
String concatenation (Execution)	5.7±0.20µs	5.9±0.23µs	-3.39%
String concatenation (Full)	194.0±7.85µs	199.5±5.37µs	-2.76%
String copy (Execution)	4.4±0.15µs	4.4±0.20µs	0.00%
String copy (Full)	190.9±8.00µs	198.6±5.27µs	-3.88%
Symbols (Execution)	3.4±0.15µs	3.5±0.12µs	-2.86%
Symbols (Full)	184.3±6.76µs	189.2±6.62µs	-2.59%