fix [#27589] Random crash with python UI

This script was defining an operator within the panels draw function, while its possible to support this its really asking for trouble.

the fix is to raise an error when this happens.

also fix crash passing non classes to register_class/unregister_class

source/blender/python/intern/bpy_rna.c

@@ -7158,8 +7158,25 @@ static PyObject *pyrna_register_class(PyObject *UNUSED(self), PyObject *py_class
 	const char *identifier;
 	PyObject *py_cls_meth;
 
+	if (!PyType_Check(py_class)) {
+		PyErr_Format(PyExc_ValueError,
+		             "register_class(...): "
+		             "expected a class argument, not '%.200s'", Py_TYPE(py_class)->tp_name);
+		return NULL;
+	}
+
 	if (PyDict_GetItem(((PyTypeObject *)py_class)->tp_dict, bpy_intern_str_bl_rna)) {
-		PyErr_SetString(PyExc_AttributeError, "register_class(...): already registered as a subclass");
+		PyErr_SetString(PyExc_ValueError,
+		                "register_class(...): "
+		                "already registered as a subclass");
+		return NULL;
+	}
+
+	if (!pyrna_write_check()) {
+		PyErr_Format(PyExc_RuntimeError,
+		             "register_class(...): "
+		             "can't run in readonly state '%.200s'",
+		             ((PyTypeObject *)py_class)->tp_name);
 		return NULL;
 	}
 
@@ -7284,12 +7301,27 @@ static PyObject *pyrna_unregister_class(PyObject *UNUSED(self), PyObject *py_cla
 	StructRNA *srna;
 	PyObject *py_cls_meth;
 
+	if (!PyType_Check(py_class)) {
+		PyErr_Format(PyExc_ValueError,
+		             "register_class(...): "
+		             "expected a class argument, not '%.200s'", Py_TYPE(py_class)->tp_name);
+		return NULL;
+	}
+
 	/*if (PyDict_GetItem(((PyTypeObject *)py_class)->tp_dict, bpy_intern_str_bl_rna) == NULL) {
 		PWM_cursor_wait(0);
 		PyErr_SetString(PyExc_ValueError, "unregister_class(): not a registered as a subclass");
 		return NULL;
 	}*/
 
+	if (!pyrna_write_check()) {
+		PyErr_Format(PyExc_RuntimeError,
+		             "unregister_class(...): "
+		             "can't run in readonly state '%.200s'",
+		             ((PyTypeObject *)py_class)->tp_name);
+		return NULL;
+	}
+
 	srna = pyrna_struct_as_srna(py_class, 0, "unregister_class(...):");
 	if (srna == NULL)
 		return NULL;