Unhandled error

Hello, I have an unhandled error with the following code:

```js
const { once, Readable } = require('stream')
const miss = require('mississippi')
const through = require('through')

const createStream = (content) => {
const s = new Readable()
s._read = () => {}
s.push(content)
s.push(null)
return s
}

;(async function () {
const transform = through(function () {
transform.emit('error', new Error('Invalid JSON (Unexpected "m" at position 1 in state STOP)'))
})
const source = createStream('No Feed.')
source.on('error', () => {
console.log('handled')
})
const stream = miss.pipeline.obj(source, transform)
const error = await once(stream, 'error')
console.log(error)
})()

```

Node: `v14.5.0`
through: `2.3.8`
pumpify: `1.5.1`

Note: I've run into this issue while using mississippi,pipeline.obj with JSONStream (see error [here](https://github.com/dominictarr/JSONStream/blob/master/index.js#L142))

Start by running the JavaScript reproduction in the issue with the listed Node, through, and pumpify versions. Trace how the emitted error moves through mississippi.pipeline.obj and compare it with the source error handler; completion would require reproducing the unhandled error and establishing the intended error propagation behavior, which the issue does not specify.

Written by the indexing model from the issue text.