Missing Non-Negative for Coin Type in LockCoins Msg

[Hellobloc]

the LockCoins Msg don't validate non-negative properties which could lead a negative subtractCoins() process in charge process, this would been a risky problem which may lead some wrong balance update and even over-minting problem.

sikkadao/x/tokenlock/keeper.go

Lines 110 to 119 in 8790121

	func (keeper Keeper) LockCoins(ctx sdk.Context, owner sdk.AccAddress, unlockTime time.Duration, amount sdk.Coins) sdk.Error {
	_, err := keeper.bankKeeper.SubtractCoins(ctx, owner, amount)
	if err != nil {
	return err
	}
	lock := keeper.GetLock(ctx, owner, unlockTime)
	lock.Amount = lock.Amount.Add(amount)
	keeper.setLock(ctx, lock)
	return nil
	}