Fix -Wempty-body warnings in Hurd-specific code.

Fix -Wempty-body warnings in Hurd-specific code.

This patch fixes -Wempty-body warnings in Hurd-specific code that show
up building glibc with -Wextra.

Note: there also such warnings on many platforms arising from the
default definition of HP_TIMING_NOW in sysdeps/generic/hp-timing.h,
but no change there is proposed in this patch because of other changes
under discussion in that area that would result in a nonempty
definition.

Tested with build-many-glibcs.py.

	* hurd/hurdinit.c (_hurd_init): Use braces around empty body of an
	if statement.