Error is thrown for wildcard paths against object with nested null values

[kostya-luxuryescape]

Hi,

Thanks a lot for the great lib.

I just wanted to raise this bug. An error is thrown in this edge case:

    const redact = fastRedact({
      paths: ['*.*.x'],
      serialize: false,
      censor: "[REDACTED]",
    });

    expect(redact({a: {b: null}})).toEqual({a: {b: null}});

Cannot use 'in' operator to search for 'x' in null
TypeError: Cannot use 'in' operator to search for 'x' in null
at specialSet (/workspace/lib-logger/node_modules/fast-redact/lib/modifiers.js:120:53)
at nestedRedact (/workspace/lib-logger/node_modules/fast-redact/lib/modifiers.js:73:7)

[kostya-luxuryescape]

I have a very simple PR to fix it ready to go: #47