Fixes #2908, add "\n" between pure literal header and function body.

before patching
```
->
  debugger
  a()
```
is compiled to
```
  (function() {
    debugger;    return a();
  });
```
this commit will add "\n" between pure literal header and function body if neither of them is empty, it will be compiled to
```
  (function() {
    debugger;    
    return a();
  });
```