Saving a file is not respecting the encoding detected with chardet

[ccordoba12]

After PR #3742, we're now detecting (and displaying) correctly files with encodings like Big5 (which is more than what Sublime and VSCode can do by default :-)

However, after doing changes to these files, Spyder is saving them as Unicode instead of respecting their encodings.

@rlaverde, please solve this one.