Low: Token URI may not be set at time of mint

[pegahcarter]

Description

When Owner calls updateBaseAssetMintPrice() to add an ERC20 BASE asset, it is not enforced that the ERC20 has an associated URI. Thus, users would be able to mint a BASE token without a token URI.t

Suggestion: Within if(previousMintPrice == 0), enforce that bytes(baseAssetTokenUris[_erc20Contract]).length > 0

[ThunderDeliverer]

Kinda similar response to #9, we'll validate that all the URIs are set before minting is live. So I wouldn't increase the smart contract size unless absolutely necessary.