node: fix #7841 by overlooking the spare sourceline

See **title** :)
I check that if it is a new line by `sourceline_string[i]`, just avoid that:
```shell
/Users/yorkie/workspace/test.js:1
(function (exports, require, module, __filename, __dirname) { /* 
                                                              ^^^^^^^
SyntaxError: Unexpected token ILLEGAL
```
The actual source file is `/*\0\0\0\0\0`(`\0` means new line), `^^` should be better, right?