doset() -> special_handling() -> free(NULL)

doset() -> special_handling() -> free(NULL)

This isn't urgent, but I figure that until the mac build stuff gets
merged in, the core is still fair game....

'O' command's autopickup_exceptions was freeing a menu pick-list even
when it hadn't been allocated (for the list case, and for the remove
case if nothing was chosen for removal).  That code was evidently used
as the model for msgtype and menucolors; they had the same situation.

I think ANSI and ISO sanction free(NULL) as a no-op, but pre-ANSI free
implementations don't necessarily handle that benignly.  Even if they
all do, freeing something--even if that 'something' is nothing--which
hasn't been allocated is a bug on our end.