dumpsys: '-l' works for 0/1 services.

Currently, if there are only 0/1 services registered and list is called,
no output will be produced.

Bug: hit me while testing vndservicemanager, since this may not register
    anything
Test: dumpsys_test
Change-Id: I8e16376eb99c5758d53ff0b5f01b32fd21e6b119