Address issues with debug allocator, and utf-8 escape sequences

[nirosys]

Issue #, if available:

Description of changes:
This PR addresses 2 issues:

• A potential integer overflow when using the debug allocator.
• Potential for uninitialized memory to be included as part of a UTF-8 escape sequence.

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[nirosys]

Looks like libasan is no longer installed by default, but this will be addressed with #366. Once it is merged, we can merge and re-run tests.

[tgregg]

Feel free to cherry-pick the libasan/libubsan changes from #366. I think that one needs to snowball a bit and I don't want to block this one.

[nirosys]

It feels like you can never know when a small change is going to wipe out an approval.. :/