Fix validation when creating GeometryCollections

[grimzy]

Closes #95

Validation:

Class	Min items	Item Type
GeometryCollection	0	GeometryInterface
(abstract) PointCollection	0 (inherited)	Point
LineString	2	Point (inherited)
MultiPoint	1	Point (inherited)
MultiLineString	1	LineString
Polygon	1 (inherited)	LineString (inherited)
MultiPolygon	1	Polygon

---

Tested with:

-- Fails with message: 'Invalid GIS data provided to function st_geomfromtext.' SET @multipt2 = ST_GeomFromText('MULTIPOINT()'); SET @line2a = ST_GeomFromText('LINESTRING(0 0)'); SET @line2b = ST_GeomFromText('LINESTRING()'); SET @multiline2a = ST_GeomFromText('MULTILINESTRING()'); SET @multiline2b = ST_GeomFromText('MULTILINESTRING((1 1))'); SET @poly2 = ST_GeomFromText('POLYGON()'); SET @multipoly2 = ST_GeomFromText('MULTIPOLYGON()'); -- Works: SET @multipt1 = ST_GeomFromText('MULTIPOINT(0 0)'); SET @line1 = ST_GeomFromText('LINESTRING(0 0, 1 1)'); -- requires 2 points SET @multiline1 = ST_GeomFromText('MULTILINESTRING((0 0, 1 1))'); SET @poly1a = ST_GeomFromText('POLYGON((0 0,10 0,10 10,0 10,0 0), (5 5,7 5,7 7,5 7, 5 5))'); SET @poly1b = ST_GeomFromText('POLYGON((0 0,10 0,10 10,0 10,0 0))'); SET @multipoly1 = ST_GeomFromText('MULTIPOLYGON(((0 0,10 0,10 10,0 10,0 0)))'); SET @geocol1a = ST_GeomFromText('GEOMETRYCOLLECTION(POINT(1 1))'); SET @geocol1b = ST_GeomFromText('GEOMETRYCOLLECTION()'); -- works while empty