Fix insert with nested json arrays and option failIfExists

[lsmacedo]

Should not try to insert multiple rows for same record.

Example, for the following object:

{
  "track": "Track",
  "artist": ["Artist 1", "Artist 2"]
}

Return the following from flattenObjectIntoArrayOfRows:

----
track: Track
artist: Artist 1
----
artist: Artist 2
----