[user-mgmt]: Handle out of range error in path

Function must assume that object path without user name may exist,
and must handle the condition accordingly.

Tested:
1. Verified when InterfacesAdded signal sent out from Phosphor-user-manager
under base user object for global attributes, ipmid is not crashed.

Resolves openbmc/phosphor-net-ipmid#10

Change-Id: Ib19af7ca8f05fd9f4553010caf347c677d9897e2
Signed-off-by: Richard Marian Thomaiyar <richard.marian.thomaiyar@linux.intel.com>
1 file changed