Explicitly use wrapping arithmetic operations when overflow may occur

[vobst]

The cwe_checker developers have mostly been compiling their code in release mode when testing it. Since dynamic overflow checks for integer arithmetic are not enabled in release mode you will encounter frequent panics when using debug builds.

For the most part, the panicking code is probably/hopefully correct. However, it should still explicitly opt-in to overflow by using the wrapping operations.

To help with this issue:

• Compile the cwe_checker in debug mode and apply it to a somewhat large program ~>= 700KiB. Chances are good that it will panic due to arithmetic overflow.
• Check the offending code and decide if it is correct or not.
• Submit a PR that either fixes the bug or changes the code to explicitly opt-in to overflow.

Thanks!