Incorrect resolution of absolute paths

Say I have a source file with URL `https://www.example.com/path/file.js` with the following sourcemap directive:

```
//# sourceMappingURL=/path/file.js.map
```

Expected behavior: `https://www.example.com/path/file.js.map` is requested.
Actual behavior: `https://www.example.com/path//path/file.js.map` is requested, which fails.