m_watch Remove dead code from remove_watch()

Found by Coverity, CID: 1130588
m_ojoin Remove pointless FindChan() call

Found by Coverity, CID: 1135649
Ignore NULL callbacks in ModuleManager::Reload()

Found by Coverity, CID: 1201453
m_auditorium Handle NULL return from Channel::GetUser() in OnSendWhoLine()

Found by Coverity, CID: 1135647