Update NetworkState in OnNetworkDestroyed instead of OnLeaveNetworkCompleted

[bschatt]

When the player lose the connection to PlayFab the Network is destroyed automatically. Since we didn't call LeaveNetwork in this case, OnLeaveNetworkCompleted will not be called. This means that the NetworkState will not be updated and it will be impossible to join or create another network as you can see in the snippet below:

PlayFabMultiplayerUnreal/Source/Private/OnlineSubsystemPlayFab.cpp

Line 688 in 3a65b08

if (NetworkState != EPlayFabPartyNetworkState::NoNetwork || Network != nullptr)

PlayFabMultiplayerUnreal/Source/Private/OnlineSubsystemPlayFab.cpp

Line 764 in 3a65b08

if (NetworkState != EPlayFabPartyNetworkState::NoNetwork || Network != nullptr)

Updating the state in OnNetworkDestroyed instead handles both cases. As stated in the comment the PartyLeaveNetworkCompletedStateChange documentation clearly states that "an associated PartyNetworkDestroyedStateChange will be generated before this state change is generated." We have been able to confirm this behavior.