Fix user/chanrecord checking on join

[vanosg]

Found by: DasBrain
Patch by: Geo

One-line summary:
Fix user/chanrecord checking on join

Additional description (if needed):
As part of the account tracking additions, we didn't properly check flag records for a user joining a channel. Thanks to lookup_user_record, this patch now universally searches for a userrecord existing before creating the new channel record and eliminates the previous per-logic-branch checks. This functionality was unaffected in post-join events (mode changes, host changes, etc).

Test cases demonstrating functionality (if applicable):

Before:

[02:42:54] #-HQ# whois geo
HANDLE                           PASS NOTES FLAGS           LAST
geo                              no       0 -               02:42 (#eggtest)
                         #eggtest           k               02:42

-----------------------------

22:42 --> Geo (user@user/geo) has joined #eggtest
22:42 -- Channel #eggtest: 2 nicks (1 op, 0 voices, 1 normal)
<end>

After:

22:43 --> Geo (user@user/geo) has joined #eggtest
22:43 -- Channel #eggtest: 2 nicks (1 op, 0 voices, 1 normal)
22:43 -- Mode #eggtest [+b *!*user@user/geo] by BeerBot
22:43 <-- BeerBot has kicked Geo (...and don't come back.)

Same for auto-op.

Also tested with a host-only user vs an account-only user, success in both cases.