prefetching for a dependent query leads to useQuery returning undefined data after query executes

[brumm]

Hey Tanner,

I think I might have found a bug involving prefetching and dependent queries.

• We prefetch a query for key 'key'
• A dependent query for key 'key' is initially not run, because the queryKey is falsy
• The falsy queryKey changes to truthy
• Expectation: The query for key 'key' returns prefetched data
• Reality: The query for key 'key' returns undefined

Here's a reproduction sandbox: https://codesandbox.io/s/react-query-bug-repro-2mxdd

This might be related to #195

[tannerlinsley]

I found the culprit. Stay tuned!

[brumm]

Dang you're fast, thanks so much!