fix: fix bug in placeLimitOrder and exchange invariant checks

[kingcre]

Description

crescent/x/exchange/keeper/order.go

Lines 150 to 162 in 92ee8b8

	if !isBatch {
	res, err = k.executeOrder(
	ctx, market, ordererAddr, isBuy, &price, &qty, nil, false, false)
	if err != nil {
	return
	}
	}
	if isBatch || qty.Sub(res.ExecutedQuantity).IsPositive() {
	deadline := ctx.BlockTime().Add(lifespan)
	order, err = k.newOrder(
	ctx, orderId, typ, market, ordererAddr, isBuy, price,
	qty, qty.Sub(res.ExecutedQuantity), deadline, false)

The bug was because we're trying to use res.ExecutedQuantity when isBatch is true. res was not set when isBatch.

Tasks

• Fix bug in placeLimitOrder
• Fix x/exchange invariant checks