RTDB emulator doesn't work properly with databaseAuthVariableOverride

### [REQUIRED] Environment info

**firebase-tools:** 8.7.0
**Platform:** macOS
**node:** v10.22.0
**firebase-admin:** 9.1.0
**firebase-database-emulator:** v4.5.0

### [REQUIRED] Test case

Add some rules like the following:

```json
{
"rules": {
"$userId": {
"publicAccess": {
".validate": "newData.isBoolean()"
},
"data": {
".read": "$userId === auth.uid || (auth.token.auth_time >= ((now / 1000) - 60 * 60) && auth.token.customClaimAccess === $userId) || data.parent().child('publicAccess').val() === true"
}
}
}
}
```

### [REQUIRED] Steps to reproduce

```js

const admin = require('firebase-admin')

const adminApp = admin.initializeApp({
databaseURL: 'https://blah.firebaseio.com',
})

const noAuthApp = admin.initializeApp({
databaseURL: 'https://blah.firebaseio.com',
databaseAuthVariableOverride: null,
}, 'no-auth')
const userAuthApp = admin.initializeApp({
databaseURL: 'https://blah.firebaseio.com',
databaseAuthVariableOverride: {
uid: 'USER_ID_1',
},
}, 'user-auth')
const customClaimsAuthApp = admin.initializeApp({
databaseURL: 'https://blah.firebaseio.com',
databaseAuthVariableOverride: {
uid: 'USER_ABC',
token: {
customClaimAccess: 'USER_ID_2',
auth_time: (Date.now() / 1000)
},
},
}, 'custom-claims-auth')

const assert = require('assert').strict

async function test() {
await adminApp.database().ref().set({
USER_ID_1: {
data: {
blah: "hello1",
},
},
USER_ID_2: {
data: {
blah: "hello2",
},
},
USER_ID_3: {
publicAccess: true,
data: {
blah: "hello3",
},
}
})

await assert.rejects(noAuthApp.database().ref('USER_ID_1/data').once('value'), /permission_denied/i, 'Should deny access with noAuthApp as not accessing public data')
await assert.doesNotReject(userAuthApp.database().ref('USER_ID_1/data').once('value'), 'Should allow access with userAuthApp as accessing own data')
await assert.doesNotReject(customClaimsAuthApp.database().ref('USER_ID_2/data').once('value'), 'Should allow access with customClaimsAuthApp as accessing data specified in claims')
await assert.doesNotReject(noAuthApp.database().ref('USER_ID_3/data').once('value'), 'Should allow access with noAuthApp as accessing public data')
}

test().catch(error => {
console.error(error)
}).finally(() => Promise.all(admin.apps.map(a => a.delete())))
```

1. Run emulator `firebase --project blah emulators:start --only database` (can't use `emulators:exec` as need to keep it running to view the rule evaluations).
2. Run the above script against the emulator `FIREBASE_DATABASE_EMULATOR_HOST=localhost:9000 node script.js`.
3. View the evaluated DB rules: `http://localhost:9000/.inspect/coverage?ns=blah`

### [REQUIRED] Expected behavior

I'd expect the tests to pass and the `auth_time` rule to be evaluated 3 times - returning `true` once and `false` twice.

### [REQUIRED] Actual behavior

Rules are not always evaluated - seems to bail out...


To simplify the case when running:

```js
await assert.rejects(noAuthApp.database().ref('USER_ID_1/data').once('value'), /permission_denied/i, 'Should deny access with noAuthApp as not accessing public data')
```

I'd expect this rule to be evaluated (as there's no `auth.uid`):
`(auth.token.auth_time >= ((now / 1000) - 60 * 60) && auth.token.customClaimAccess === $userId) || data.parent().child('publicAccess').val() === true`


The whole rule seems not to be evaluated, despite the first rule being evaluated...!



Start the database emulator with `firebase --project blah emulators:start --only database`, then run the supplied Node.js reproduction with `FIREBASE_DATABASE_EMULATOR_HOST=localhost:9000`. Inspect the evaluated rules at `/.inspect/coverage?ns=blah`; done means all four assertions pass and the `auth_time` rule is evaluated three times, returning true once and false twice.

Written by the indexing model from the issue text.