graphql: fix an issue of nil pointer panic

[jsvisa]

Fix as issue of nil pointer panic

query

{blocks { number }}

response

{
  "errors": [
    {
      "message": "panic occurred: runtime error: invalid memory address or nil pointer dereference",
      "path": [
        "blocks"
      ]
    }
  ],
  "data": null
}

and the stack:

> 2023/10/26 08:25:36 graphql: panic occurred: runtime error: invalid memory address or nil pointer dereference
goroutine 4252 [running]:
github.com/graph-gophers/graphql-go/log.(*DefaultLogger).LogPanic(0x28?, {0x104254960?, 0x140014805a0}, {0x103fdb9a0, 0x104d31bf0})
        github.com/graph-gophers/graphql-go@v1.3.0/log/log.go:21 +0x58
github.com/graph-gophers/graphql-go/internal/exec.execFieldSelection.func2.1()
        github.com/graph-gophers/graphql-go@v1.3.0/internal/exec/exec.go:187 +0x80
panic({0x103fdb9a0?, 0x104d31bf0?})
        runtime/panic.go:914 +0x218
github.com/ethereum/go-ethereum/graphql.(*Resolver).Blocks(0x140014a6210, {0x104254960, 0x14001480630}, {0x0?, 0x0?})
        github.com/ethereum/go-ethereum/graphql/graphql.go:1327 +0x30
reflect.Value.call({0x104159a60?, 0x140014a6210?, 0x1400075ac68?}, {0x10386365d, 0x4}, {0x14001480660, 0x2, 0x103391400?})
        reflect/value.go:596 +0x994
reflect.Value.Call({0x104159a60?, 0x140014a6210?, 0x104253590?}, {0x14001480660?, 0x10422b220?, 0x1b?})
        reflect/value.go:380 +0x94
github.com/graph-gophers/graphql-go/internal/exec.execFieldSelection.func2(0x1400064c638?, {0x104254960?, 0x140014805a0?}, 0x14000b760c0, 0x14001490140, 0x140009a3eb0, {0x104254960?, 0x14001480630})
        github.com/graph-gophers/graphql-go@v1.3.0/internal/exec/exec.go:211 +0x380
github.com/graph-gophers/graphql-go/internal/exec.execFieldSelection({0x104254960, 0x140014805a0}, 0x1400101c100, 0x0?, 0x14001490140, 0x0?, 0x1)
        github.com/graph-gophers/graphql-go@v1.3.0/internal/exec/exec.go:231 +0x118
github.com/graph-gophers/graphql-go/internal/exec.(*Request).execSelections.func1(0x14001490140)
        github.com/graph-gophers/graphql-go@v1.3.0/internal/exec/exec.go:81 +0x178
created by github.com/graph-gophers/graphql-go/internal/exec.(*Request).execSelections in goroutine 4250
        github.com/graph-gophers/graphql-go@v1.3.0/internal/exec/exec.go:77 +0x140

context: context.Background.WithValue(type *http.contextKey, val <not Stringer>).WithValue(type *http.contextKey, val 127.0.0.1:8545).WithCancel.WithCancel.WithCancel.WithValue(type opentracing.contextKey, val <not Stringer>)

@s1na PTAL

[s1na]

The default values that make sense would be 0 or like last finalized block. But 0 can be too long a range and finalized is rather arbitrary. I agree best to return an error. We should make a list of all these errors to standardize.

[s1na]

SGTM