[fix] register prevent re-registering

__init__.py

@@ -23,13 +23,15 @@ Classes = (BLENDERGPT_PT_PANEL, BLENDERGPT_OT_DEL_ALL_MSG, BLENDERGPT_OT_DEL_MSG
 
 def register():
     for cls in Classes:
-        bpy.utils.register_class(cls)
+        if cls.__name__ not in bpy.types.__dict__:
+            bpy.utils.register_class(cls)
 
     props_initialization()
 
 
 def unregister():
     for cls in Classes:
-        bpy.utils.unregister_class(cls)
+        if cls.__name__ in bpy.types.__dict__:
+            bpy.utils.unregister_class(cls)
 
     props_clear()