On some systems, typing ^C apparently results in a KEY_CANCEL in
the input stream, which gets hard-bound to the do_cancel function.
But in the main menu there is no Cancel function.  So... in that
case, let it fall back to the plain old Ctrl-C code: 0x03.
Reported-by: Liam Gretton <liam.gretton@leicester.ac.uk>