Add invalid WKB case

Author: jiayuasu

Geospatial.md

@@ -212,4 +212,6 @@ calculations.
   include `LineString` with no coordinates (hex: `01 02 00 00 00 00 00 00 
   00`) or `Polygon` with no coordinates (hex: `01 03 00 00 00 00 00 00 00`).
 * `Out-of-bounds coordinates`: Values that fall outside the valid range 
-  for `GEOGRAPHY` types. For example, `x < -180` or `x > 180`.
+  for `GEOGRAPHY` types. For example, `x < -180` or `x > 180`.
+* Any invalid WKB representation of a geospatial instance, such as an empty 
+  string.