graphql: return error if block from>to (#28393)

As per discussion in ethereum/execution-apis#475

graphql/graphql.go

@@ -42,6 +42,7 @@ import (
 
 var (
 	errBlockInvariant    = errors.New("block objects must be instantiated with at least one of num or hash")
+	errInvalidBlockRange = errors.New("invalid from and to block combination: from > to")
 )
 
 type Long int64
@@ -1333,7 +1334,7 @@ func (r *Resolver) Blocks(ctx context.Context, args struct {
 		to = rpc.BlockNumber(r.backend.CurrentBlock().Number.Int64())
 	}
 	if to < from {
-		return []*Block{}, nil
+		return nil, errInvalidBlockRange
 	}
 	var ret []*Block
 	for i := from; i <= to; i++ {