This `pdb.Pdb.init` call can return `error.FileNotFound`, which was previously resulting in:

    Unable to print stack trace: FileNotFound

which also aborts the stack trace printing (so any deeper stack traces are not printed).

It makes more sense to treat it as `MissingDebugInfo` which then gets printed as:

    ???:?:?: 0x7fffa8817033 in ??? (???)

and allows the stack trace to continue printing.

Note: locally, the error.FileNotFound was being triggered for me when looking for kernel32.pdb and ntdll.pdb