CBattleInterface: fix crash on defeat in tactics phase. Fix issue 2440

It's possible to lose all mobile stacks if you move them on moat so tactics phase must end in that case.

client/battle/CBattleInterface.cpp

@@ -1935,6 +1935,12 @@ void CBattleInterface::bTacticNextStack(const CStack *current /*= nullptr*/)
 
 	TStacks stacksOfMine = tacticianInterface->cb->battleGetStacks(CBattleCallback::ONLY_MINE);
 	vstd::erase_if(stacksOfMine, &immobile);
+	if(stacksOfMine.empty())
+	{
+		bEndTacticPhase();
+		return;
+	}
+
 	auto it = vstd::find(stacksOfMine, current);
 	if(it != stacksOfMine.end() && ++it != stacksOfMine.end())
 		stackActivated(*it);