Fix path.format compatibility issue.

[Hanaasagi]

What does this PR do?

1. Check if the argument is an empty string in path.format. Close: path.format({base: ''}) inconsistency with Node #4005
2. Avoid duplicating '/' at the beginning of the path. Fix following code.

const path = require("node:path");
const assert = require("node:assert");
assert.strictEqual(
  path.format({
    root: "/",
    name: "file",
    ext: ".txt",
  }),
  "/file.txt",
);

In Bun 0.7.3

AssertionError: Expected values to be strictly equal:
+ actual - expected

+ '//file.txt'
- '/file.txt'

• 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 ran make js and committed the transpiled changes
• I or my editor ran Prettier on the changed files (or I ran bun fmt)
• I included a test for the new code, or an existing test covers it

[Jarred-Sumner]

Thank you