Use g_memdup2, which avoids overflow on the size argument.

Index: gschem/src/gschem_page_geometry.c
--- gschem/src/gschem_page_geometry.c.orig
+++ gschem/src/gschem_page_geometry.c
@@ -52,7 +52,7 @@ update_constants (GschemPageGeometry *geometry);
 GschemPageGeometry*
 gschem_page_geometry_copy (GschemPageGeometry *geometry)
 {
-  return (GschemPageGeometry*) g_memdup (geometry, sizeof (GschemPageGeometry));
+  return (GschemPageGeometry*) g_memdup2 (geometry, sizeof (GschemPageGeometry));
 }
 
 
