entities: fix Destroy() not being called in some cases (#139)

when a player disconnects and is replaced by a bot, the bot may have the
same entity-ID as the player.
also the player's entity may not have been destroyed, since the
PVS-leave update was never sent.
for this case we need to make sure old entities are destoryed before
calling ReadEnterPVS().

Author: markus-wa

entities.go

@@ -33,6 +33,11 @@ func (p *Parser) handlePacketEntities(pe *msg.CSVCMsg_PacketEntities) {
 			r.ReadBit()
 		} else if r.ReadBit() {
 			// Enter PVS
+			if existing := p.gameState.entities[currentEntity]; existing != nil {
+				// Sometimes entities don't get destroyed when they should be
+				// For instance when a player is replaced by a BOT
+				existing.Destroy()
+			}
 			p.gameState.entities[currentEntity] = p.stParser.ReadEnterPVS(r, currentEntity)
 		} else {
 			// Delta Update