check send_signal result before further dealing

If send_signal failed, debuggerd_trigger_dump should return
instead of further dealing

Change-Id: I0a1ac4255344d1da7a21917ad559b9de4d5a4fee
Signed-off-by: Liu Changcheng <changcheng.liu@intel.com>
Signed-off-by: Jerry Liu <primerlink@gmail.com>