librc/librc-depend.c: fix NULL pointer dereference
librc/librc-depend.c: fix NULL pointer dereference

In some cases deptree or depinfo can be NULL, check
before dereferencing.

Fixes https://github.com/OpenRC/openrc/issues/293
Fixes https://github.com/OpenRC/openrc/pulls/294
X-Gentoo-Bug: 659906
X-Gentoo-Bug-URL: https://bugs.gentoo.org/659906

williamh/openrc,OpenRC/openrc,williamh/openrc,OpenRC/openrc,OpenRC/openrc,williamh/openrc