curses_yn_function() was returning a value that wasn't in the
subset of legal return values. This fixes that.
The unexpected return value of 32 (or space) then brought to
light an indexing error in the core that's been there a while,
apparently since at least 3.2.0, and that caused a null pointer
dereference in a strlen() call, which is what actually caused
the crash in issue #1205. This fixes that too.
Close#1205
3a9e53a629