JSON decode fails if buf empty

[oanatmaria]

If result is

{
  "results": [],
  "objects": {},
  "page": {
    "next_token": ""
  }
}

ast.ValueFromReader fails to decode empty buf

[github-actions]

Pull Request Test Coverage Report for Build 6771663773

• 0 of 2 (0.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage remained the same at 41.792%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
builtins/edge/ds/relation.go	0	2	0.0%

Files with Coverage Reduction	New Missed Lines	%
builtins/edge/ds/relation.go	1	30.0%

Totals
Change from base Build 6766369268:	0.0%
Covered Lines:	1413
Relevant Lines:	3381

---

💛 - Coveralls