Avoid mixing void and integer in a conditional expression.

Avoid mixing void and integer in a conditional expression.

The C standard says that the second and third arguments of a
conditional operator shall be both void type or both not-void
type.  The Windows version of INTERRUPTS_PENDING_CONDITION()
got this wrong.  It's pretty harmless because the result of
the operator is ignored anyway, but apparently recent versions
of MSVC have started issuing a warning about it.  Silence the
warning by casting the dummy zero to void.

Reported-by: Christian Ullrich <chris@chrullrich.net>
Author: Bryan Green <dbryan.green@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/cc4ef8db-f8dc-4347-8a22-e7ebf44c0308@chrullrich.net
Backpatch-through: 13