ignore_malformed doesn't always work for invalid geoJSON

[Lumaraf]

Elasticsearch version:
6.2.3

JVM version:
1.8.0_161

OS version
Debian 4.9.30-2+deb9u2

Description of the problem including expected versus actual behavior:
For geo_shape fields ignore_malformed:true does not work if the coordinates field contains on object or an array with only one element. Instead of not indexing the field a mapper_parsing_exception is returned and the document is not stored.

Steps to reproduce:

1. create index with a geo_shape field

{
    "mappings": {
        "docs": {
            "properties": {
                "location": {
                    "type": "geo_shape",
                    "ignore_malformed":true
                }
            }
        }
    }
}

2. insert one of the follwing documents containing invalid GeoJSON

{
  "location": {
    "type": "point",
    "coordinates": {}
  }
}

{
  "location": {
    "type": "point",
    "coordinates": [0]
  }
}

[elasticmachine]

Pinging @elastic/es-search-aggs