Value.Patch: "add" with an out-of-range array index appends instead of failing

[RaphaelFakhri]

What happened

An add operation whose array index is greater than the array length succeeds and appends the value.

v, _ := hujson.Parse([]byte(`[1,2]`))
err := v.Patch([]byte(`[{"op":"add","path":"/5","value":3}]`))
fmt.Println(err, string(v.Pack()))
// <nil> [1,2,3]

What you expected

RFC 6902, section 4.1 states that the index of an add on an array must not be greater than the number of elements. The patch should fail with an error and leave the array unchanged. Indexes equal to the length and the - token continue to append.

Cause

patchAdd in patch.go accepts any errNotFound from find as an insertion point. For arrays, find reports the array length as the index for every missing index, so /5 is treated the same as /2 or /-.