extra safety

rts/Sim/Units/CommandAI/FactoryCAI.cpp

@@ -309,6 +309,7 @@ bool CFactoryCAI::RemoveBuildCommand(CCommandQueue::iterator& it)
 void CFactoryCAI::DecreaseQueueCount(const Command& buildCommand, BuildOption& buildOption)
 {
 	// copy in case we get pop'ed
+	// NOTE: the queue should not be empty at this point!
 	const Command frontCommand = commandQue.empty()? Command(CMD_STOP): commandQue.front();
 
 	if (!repeatOrders || (buildCommand.options & DONT_REPEAT))
@@ -322,7 +323,11 @@ void CFactoryCAI::DecreaseQueueCount(const Command& buildCommand, BuildOption& b
 	if (frontCommand.GetID() == CMD_WAIT)
 		commandQue.pop_front();
 
-	FinishCommand();
+	// can only finish the real build-command command if
+	// we still have it in our queue (FinishCommand also
+	// asserts this)
+	if (!commandQue.empty())
+		FinishCommand();
 
 	if (frontCommand.GetID() == CMD_WAIT)
 		commandQue.push_front(frontCommand);