(operserv/rwatch.c) Fix null ptr dereference

Reaudited my bug fixes from the other day and noticed that I had neglected to check for null before dereferencing a potentially null pointer. Oops.
Merge pull request #288 from partedcloud/patch-1

(operserv/rwatch.c) Fix null ptr dereference
operserv/rwatch: More fixes to legacy db load
Check correct function pointer before invocation
Allow sourceinfo to replace command_success_table impl.