geo_point parsing doesn't ignore malformed points represented as a string

[imotov]

Looks like there are some use cases in #16137 that were not fully addressed in #16833. In particular, some values in string presentation of a geo_point are not handled correctly. To reproduce:

DELETE example

PUT example
{
    "mappings": {
        "doc": {
            "properties": {
                "location": {
                    "type": "geo_point",
                    "ignore_malformed": true
                }
            }
        }
    }
}

PUT example/doc/1
{
  "location": "NaN,NaN"
}

PUT example/doc/2
{
  "location": "-,-"
}