Queries with multiple roots doesn't produce a population object

[hennessyevan]

Describe the bug
Querying two models at once returns no population object.

To Reproduce
Use a query like this:

query Multiple {
  first {
    child {
      foo
    }
  }
  second {
    child {
      bar
    }
  }
}

console.log(registry.populate(info, First.modelName)) // -> []

Expected behavior
It should return population object for path.

console.log(registry.populate(info, First.modelName)) // -> [{ path: 'child', populate: [], select: ['id', 'foo'] }]

Desktop (please complete the following information):

• OS: macOS 10.15
• NodeJS Version: 10.16.3
• GraphQL Version: 14.5.8
• Mongoose Version: 5.7.5