Thanks for the bug report. I installed the attached more-adventurous patch, 
which truncates the result rather than extending it with nils. This seems a bit 
more appropriate anyway.

Although it no longer matters for this patch, memclear is specified to store nil 
values regardless of how nil is represented. Of course memclear's current 
implementation assumes Qnil is zero, and memclear can't be portably and easily 
implemented if we merely change Qnil to be nonzero, but that's a bridge we don't 
have to cross unless we change Qnil to be nonzero.