Prevent fail on u8 overflow

[oxade]

This fixes #417

Rust will panic if overflow occurs in debug mode. u8 has relatively low probability of being 255 after a test run, hence the difficulty reproduce.
This fix subtracts instead of adds if at u8::MAX. The goal here is to create an offending object id, so it doesn't matter if add or subtract

[lxfind]

Is there something special about the object ID right after the gas object ID? Trying to understand what it is trying to test.

[oxade]

Is there something special about the object ID right after the gas object ID? Trying to understand what it is trying to test.

I think it's just checking that the logic fails as expected for unknown objects

[lxfind]

Is there something special about the object ID right after the gas object ID? Trying to understand what it is trying to test.

I think it's just checking that the logic fails as expected for unknown objects

In that case, you could do something simple like u8::MAX - x[last_index]

[oxade]

Is there something special about the object ID right after the gas object ID? Trying to understand what it is trying to test.

I think it's just checking that the logic fails as expected for unknown objects

In that case, you could do something simple like u8::MAX - x[last_index]

Indeed that concise. But 1AM brain did not see it lol