Fix rare crash bug in SDKTools GetGameRulesProxyEnt

[BotoX]

https://github.com/ValveSoftware/source-sdk-2013/blob/0d8dceea4310fde5706b3ce1c70609d72a38efdf/mp/src/game/server/ServerNetworkProperty.cpp#L157

ServerClass* CServerNetworkProperty::GetServerClass()
{
	if ( !m_pServerClass )
		m_pServerClass = m_pOuter->GetServerClass();
	return m_pServerClass;
}

m_pOuter can be NULL and then GetServerClass would crash
so check m_pOuter first with GetEntityHandle:

IHandleEntity *CServerNetworkProperty::GetEntityHandle( )
{
	return m_pOuter;
}

https://github.com/ValveSoftware/source-sdk-2013/blob/0d8dceea4310fde5706b3ce1c70609d72a38efdf/mp/src/game/server/ServerNetworkProperty.cpp#L103

Using GameRules_SetProp would sometimes crash for us, after this fix it hasn't crashed for 2 weeks and it doesn't look wrong to check this either.

[KyleSanderson]

Sorry man - thank you very much for the patch and crash fix.