[examples]: GRC20 underflow/overflow checking

[MalekLahbib]

Description

@moul, I was checking the grc20 package, and in banker.gno file you put // TODO: check for overflow in the Mint and Burn functions.
I added the check in Mint function and added a test file.

but I don't see why (or how) to check for overflow in Burn function, as the check in Mint function is enough to protect from overflow.

[leohhhn]

Can you please link the specific files you're talking about?

[MalekLahbib]

Can you please link the specific files you're talking about?

I updated my comment.

[leohhhn]

Thanks.

I think the idea here was to check for underflow in the case of burn.

[MalekLahbib]

I created this PR2874.

[leohhhn]

Cool, I'll take a look. Thanks.

In the future, please try to make your PRs & issues a bit more descriptive, so that the person reading it has the context needed to understand. This also applies to issue/PR names :)