[OGR provider] Do not return wkbUnknown25D, wkbUnknownM/Z/ZM layer ge…

…ometry types

Those are illegal QgsWKBTypes::Type / QGis::WkbType values, and can cause
undefined behaviour outside of the provider.

Fixes #15064

src/providers/ogr/qgsogrprovider.cpp

@@ -699,6 +699,11 @@ OGRwkbGeometryType QgsOgrProvider::getOgrGeomType( OGRLayerH ogrLayer )
   {
     geomType = OGR_FD_GetGeomType( fdef );
 
+    // Handle wkbUnknown and its Z/M variants. QGIS has no unknown Z/M variants,
+    // so just use flat wkbUnknown
+    if ( wkbFlatten( geomType ) == wkbUnknown )
+      geomType = wkbUnknown;
+
     // Some ogr drivers (e.g. GML) are not able to determine the geometry type of a layer like this.
     // In such cases, we use virtual sublayers for each geometry if the layer contains
     // multiple geometries (see subLayers) otherwise we guess geometry type from first feature