Fix a minor crash when a user has no class after OnCheckReady.

Fix a minor crash when a user has no class after OnCheckReady.

This bug looks serious but it can only be triggered with a
very unusual server configuration problem. If you haven't
already had a crash then you probably aren't at any risk.

The way this crash happens is:

1. InspIRCd::DoBackgroundUserStuff is called by the main loop.
2. In the switch statement curr->registered is set to REG_NICKUSER so InspIRCd::AllModulesReportReady is called.
3. InspIRCd::AllModulesReportReady calls the OnCheckReady event in m_cgiirc.
4. m_cgiirc calls RecheckClass which sets the user's class to NULL and calls LocalUser::SetClass followed by LocalUser::CheckClass.
5. The user doesn't match any classes in LocalUser::SetClass so LocalUser::CheckClass quits the user with with "Access denied by configuration".
6. Control flow returns to InspIRCd::DoBackgroundUserStuff when InspIRCd::AllModulesReportReady returns false.
7. The if statement at the end of InspIRCd::DoBackgroundUserStuff calls ConnectClass::GetRegTimeout on curr->MyClass.
8. ConnectClass::GetRegTimeout tries to access a member of this which is NULL.
9. The server crashes with a SEGFAULT.