Fix dirfd crash issue in property service

In "init: harden property service" patch, dirfd() is invoked
without checking whether opendir() return successfully. It may
fail if load_persistent_properties() is invoked before userdata
partition is mounted; then dirfd(NULL) will make init crash.
This may happen if "is_charger" is true.

Change-Id: I216fb743a3c9fa050f92fcb31b62e766346d84bb
Signed-off-by: Yi-wei Zhao <gbjc64@motorola.com>