Handle undefined queryClient when passed as thunk

[hmnd]

Currently, the queryClient param is optional, but this doesn't account for a query-creating function like this, where the queryClient is optional. This PR allows undefined to be returned, since undefined is already expected and supported in useQueryClient.

function createMyQuery(ctx: () => { queryClient?: QueryClient }) {
  return createQuery(() => ({
    queryKey: ['mykey'],
    queryFn: () => ({ myreturn: 'cool' }),
  }), () => ctx?.().queryClient); // queryClient returned here may be undefined 
}