Data undefined from useQuery when using pagination

[harryfpayne]

I've noticed flickering on paginated queries when I upgraded to urql version 2.1.2 from 2.0.6.

Here's a minimal example:

export default function Home() {
  const [args, setArgs] = useState<{take: number, offset: number}>({take: 10, offset: 0});
  const [{ data, fetching }] = useQuery<{ getAllPokemonSpecies: string[] }>({
    query: `query ($take: Int!, $offset: Int!){
      getAllPokemonSpecies(offset: $offset, take: $take)
    }`,
    variables: args,
  });

  function fetchMore() {
    setArgs(p => ({...p, offset: p.offset + p.take}))
  }

  return (
    <div>
      {(data === undefined || data.getAllPokemonSpecies.length === 0 )? (
        <div>No pokemon</div>
      ) : (
        <>
          {data.getAllPokemonSpecies.map(pokemon => (
              <div key={pokemon}>{pokemon}</div>
          ))}
        </>
      )}
      <button onClick={fetchMore}>Load 10 more</button>
    </div>
  )
}

With the provider defined as:

const cache = cacheExchange({
  resolvers: {
    Query: {
      getAllPokemonSpecies: simplePagination({limitArgument: "take", offsetArgument: "offset", mergeMode: "after"}),
    },
  },
});

export const client = createClient({
  url: "https://graphqlpokemon.favware.tech/",
  exchanges: [dedupExchange, refocusExchange(), cache, fetchExchange],
});

export function GraphqlProvider({ children }) {
  return <Provider value={client}>{children}</Provider>;
}

When I'm using version 2.1.2 the list will flicker back to 'No pokemon' while fetching, this doesn't match the behaviour of 2.0.6

I made a minimal demo app to demonstrate: https://github.com/harryfpayne/urql-pagination-bug.
You should find that downgrading to version 2.0.6 will stop the flickering while fetching

urql version:
urql 2.1.2

Steps to reproduce:

1. fetch while using simplePagination
2. Observe the data returned from useQuery is undefined while the request is fetching

Expected behavior
The previous state should persist while the request is being performed, this happens in version 2.0.6

Actual behavior
The data is undefined while the request is being performed

[JoviDeCroock]

This should be fixed in 2.1.3, feel free to reopen if the issue persists, the linked PR's contain the reproduction used