pure-ftpd: add patch that fixes build if HAVE_EXPLICIT_BZERO is defined

This patch was already merged upstream and once bumping version of that
package this patch must be removed.

See this change upstream:
https://github.com/jedisct1/pure-ftpd/commit/2d34799585dc65c8c314a2f09a281874dd9b3d55



Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>