Should work when the exception doesn't have a backtrace

[JoshCheek]

In #134 there was a bug in Ruby where the exception didn't have a backtrace (I think because it never got raised, it just got set somehow, so then it went into the at_exit block which passed it to the lib).

Prob no way to truly this without writing C code (since I'll need to override the methods with refinements, anyway), and it is just compensating for a bug in the interpreter, but still, it shouldn't explode when this happens.

• Doesn't explode when Exception#backtrace returns nil
• Maybe it should use the Safe refinements in the matrix?
• Tangentially related: maybe try a test where it just straight deletes every method off of every class and show that it still works. That might be the best way to avoid regressions from hostile environments that I haven't thought of?