lavfi/pad: avoid buffer overflow in buffer_needs_copy()

Replace & with short-circuit &&.

Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
mem: Fix usage of memalign() on DJGPP.

Credits to Khusraw of bttr-software.de forum.
Signed-off-by: Carl Eugen Hoyos <cehoyos@ag.or.at>