launch/nss-cache: avoid macro repetition
launch/nss-cache: avoid macro repetition

Avoid repetition of the C_ARRAY_SIZE() macro and use a local constant
instead. This silences warnings of gcc which otherwise cannot detect the
early function return for `n_usernames == 0`.

Signed-off-by: David Rheinsberg <1e7ff67ac6e6692b085f67edeb10803d9022c525@gmail.com>

bus1/dbus-broker