Fix Cycles missing geometry header in object header, causing crashes

The problem is that `set_geometry()` otherwise ends up implicitly
casting `Geometry*` to bool. In Blender this worked because the
geometry header was always included before the object header.

Differential Revision: https://developer.blender.org/D16737

intern/cycles/scene/object.h

@@ -9,6 +9,7 @@
 /* included as Object::set_particle_system defined through NODE_SOCKET_API does
  * not select the right Node::set overload as it does not know that ParticleSystem
  * is a Node */
+#include "scene/geometry.h"
 #include "scene/particles.h"
 #include "scene/scene.h"