util/build-id: check dlpi_name before strstr call

util/build-id: check dlpi_name before strstr call

According to dl_iterate_phdr man page first object visited is the
main program where dlpi_name is an empty string. This fixes segfault
on Android when using build-id as identifier.

Fixes: d4fa083e11f ("util: Add utility build-id code.")
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Plamena Manolova <plamena.manolova@intel.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>