emjsfile access: Improve documentation and error handling
This MR is a follow-up on @robUx4's review on !2149 (merged)
List of changes :
- Add/fix documentation for the RangeError on BigUint64 views.
- Handles missing close if get_js_file_size failed.
- fix warning for wrong field type js_file_size.
- remove whitespaces and an outdated comment.
Edited by Mehdi Sabwat