Reduce repeated checks in the SupplyLogic.sol

[tanliwei]

Merge two if branches into a two-level if branches to save gas without changing the logic.

The only case in this PR not covered is when the passed-in parameter params.amount equal to userBalance that is IAToken(reserveCache.aTokenAddress).scaledBalanceOf(msg.sender).rayMul(reserveCache.nextLiquidityIndex);

This pr is ok if only the value type(uint256).max stands for withdraw all asset.

[height]

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