Gameserver: don't interpret NETMSG_STARTPLAYING

[sprunk]

The code is incorrect (path always leads to assertion), nothing actually sends this, and nothing should send it because the way to start by a local player is /forcestart rather than a packet.

[sprunk]

Always asserts due to gameHasStarted:

RecoilEngine/rts/Net/GameServer.cpp

Lines 1464 to 1466 in 5585868

	case NETMSG_STARTPLAYING: {
	if (players[a].isLocal && gameHasStarted)
	CheckForGameStart(true);

RecoilEngine/rts/Net/GameServer.cpp

Lines 2135 to 2137 in 5585868

	void CGameServer::CheckForGameStart(bool forced)
	{
	assert(!gameHasStarted);

Proper way to do this is already /forcestart:

RecoilEngine/rts/Net/GameServer.cpp

Lines 2441 to 2443 in 66de25f

	case hashString("forcestart"): {
	if (!gameHasStarted)
	CheckForGameStart(true);