Fix path.normalize edge case.

[Hanaasagi]

Close: #4041

What does this PR do?

path.normalize(""): If the path is a zero-length string, '.' is returned, representing the current working directory.

• Documentation or TypeScript types (it's okay to leave the rest blank in this case)
• Code changes

How did you verify your code works?

I wrote automated tests

• I checked the lifetime of memory allocated to verify it's (1) freed and (2) only freed when it should be
• I or my editor ran zig fmt on the changed files
• I included a test for the new code, or an existing test covers it
• JSValue used outside outside of the stack is either wrapped in a JSC.Strong or is JSValueProtect'ed

[Jarred-Sumner]

Thank you