[PostGIS] #5718: `st_isvalid(point(NaN, NaN))` is true

[PostGIS]

#5718: `st_isvalid(point(NaN, NaN))` is true
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  Reporter:  n0099    |      Owner:  pramsey
      Type:  defect   |     Status:  new
  Priority:  medium   |  Milestone:
 Component:  postgis  |    Version:  3.4.x
Resolution:           |   Keywords:
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Comment (by mdavis):

 The [https://www.geopackage.org/spec/ GeoPackage spec] also specifies the
 same approach:

 > If the geometry is a Point, it SHALL be encoded with each coordinate
 value set to an IEEE-754 quiet NaN value. GeoPackages SHALL use big endian
 0x7ff8000000000000 or little endian 0x000000000000f87f as the binary
 encoding of the NaN values. (This is because Well-Known Binary as defined
 in OGC 06-103r4 [I9] does not provide a standardized encoding for an empty
 point set, i.e., 'Point Empty' in Well-Known Text.)
-- 
Ticket URL: <https://trac.osgeo.org/postgis/ticket/5718#comment:5>
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