Fix /l and /unlock, uniform undef. target returns

If the target of /lock and /unlock doesn't exist, they return "User undefined not found."
Also made all the mod commands with targets that don't exist return the same message as /roomban does for consistency.

Bring back change from commit d1ed6f7

Actual d1ed6f7, /unlock and /unban offline users

Fix /l and /unlock, uniform undef. target returns
Merge pull request #955 from Morfent/patch-2

Fix /l and /unlock, uniform undef. target returns