bugfix(replay): Stop dereferencing a null slot when a replay has no local player

[bobtista]

• Closes Replay playback dereferences a null slot when the local player index is -1 #3239

A replay whose local player index is -1 dereferenced a missing slot in two places. RecorderClass::playbackFile read the local slot to tell a network game from a local one, and GameLogic::startNewGame read it again to mark the local player. readReplayHeader accepts -1 and GameInfo::getSlot returns nullptr for a negative slot, so such a replay crashed before it could play.

Now the replay CRC queue is primed from the recorded game mode, which answers the network question directly and keeps the CRC alignment a network replay needs, and the local slot lookup during game start treats a missing local slot as no slot being local.

Verified with a replay byte-edited to carry -1: it crashes before the change and plays to completion after it. Twelve unmodified replays produce identical CRC results before and after.

Todo:

• Both games build (z_generals and g_generals)
• Replicate to Generals
• Replay with no local player crashes before the change
• Replay with no local player plays to completion after the change
• Unmodified replays report identical CRC results before and after

[Caball009]

FWIW, GeneralsOnline does something similar: https://github.com/GeneralsOnlineDevelopmentTeam/GameClient/blob/fde347843c9c393716667ba4cee8afad1b276d45/GeneralsMD/Code/GameEngine/Source/Common/Recorder.cpp#L1198-L1200