fix ALT+N

[MCWertGaming]

Even after the fix of the alt and ctrl keys ALT+N remains broken. I'm not sure yet what's exactly the problem, but it's inside of the utf8_to_utf32() functions because it's throwing a runtime_error when you press it. The console output is:

[mcwertgaming@archlinux examples]$ /home/mcwertgaming/git/cpp-terminal/build/examples/prompt
Interactive prompt.
  * Use Ctrl-D to exit.
  * Use Enter to submit.
  * Features:
    - Editing (Keys: Left, Right, Home, End, Backspace)
    - History (Keys: Up, Down)
    - Multi-line editing (use Alt-Enter to add a new line)
> Runtime error: Expected more bytes in UTF8 encoded string                                                                                                                                                                                                                        1,1   ]
[mcwertgaming@archlinux examples]$