Fixed: Incorrect SpawnPotentials structure when adjusting spawn posit…

…ions during copy and import.

Described in mcedit/mcedit#347

entity.py

@@ -103,15 +103,15 @@ def copyWithOffset(cls, tileEntity, copyOffset):
                 mobs.append(mob)
             potentials = eTag.get('SpawnPotentials')
             if potentials:
-                mobs.extend(potentials)
+                mobs.extend(p["Properties"] for p in potentials)
 
             for mob in mobs:
                 if "Pos" in mob:
                     pos = Entity.pos(mob)
                     pos = [p + o for p, o in zip(pos, copyOffset)]
 
                     Entity.setpos(mob, pos)
-                    
+
         if eTag['id'].value == "Control":
             command = eTag['Command'].value