xcvrd exception in transceiver eeprom during OIR

[brandonchuang]

Symptoms:

1. It takes around 10 seconds to read the eeprom of the transceiver with pages. sfp_optoe_base reads the eeprom too many times.
2. The exception occurs when a transceiver is plugged in then unplugged within 10 seconds.
3. If the transceiver is unplugged 10 seconds later, the the exception won't happen.

Exception in thread Thread-1:
Traceback (most recent call last):
File "/usr/lib/python3.7/threading.py", line 917, in _bootstrap_inner
self.run()
File "/usr/lib/python3.7/threading.py", line 865, in run
self._target(*self._args, **self._kwargs)
File "/usr/local/lib/python3.7/dist-packages/xcvrd/xcvrd.py", line 1366, in task_worker
post_port_dom_info_to_db(logical_port_name, self.port_mapping, xcvr_table_helper.get_dom_tbl(asic_index), self.task_stopping_event, dom_info_cache=dom_info_cache)
File "/usr/local/lib/python3.7/dist-packages/xcvrd/xcvrd.py", line 434, in post_port_dom_info_to_db
dom_info_dict = _wrapper_get_transceiver_dom_info(physical_port)
File "/usr/local/lib/python3.7/dist-packages/xcvrd/xcvrd.py", line 154, in _wrapper_get_transceiver_dom_info
return platform_chassis.get_sfp(physical_port).get_transceiver_bulk_status()
File "/usr/local/lib/python3.7/dist-packages/sonic_platform_base/sonic_xcvr/sfp_optoe_base.py", line 28, in get_transceiver_bulk_status
return api.get_transceiver_bulk_status() if api is not None else None
File "/usr/local/lib/python3.7/dist-packages/sonic_platform_base/sonic_xcvr/api/public/cmis.py", line 205, in get_transceiver_bulk_status
self.vdm_dict = self.get_vdm()
File "/usr/local/lib/python3.7/dist-packages/sonic_platform_base/sonic_xcvr/api/public/cmis.py", line 1015, in get_vdm
vdm = self.vdm.get_vdm_allpage() if not self.is_flat_memory() else {}
File "/usr/local/lib/python3.7/dist-packages/sonic_platform_base/sonic_xcvr/api/public/cmisVDM.py", line 178, in get_vdm_allpage
vdm_current_page = self.get_vdm_page(page, vdm_flag_page)
File "/usr/local/lib/python3.7/dist-packages/sonic_platform_base/sonic_xcvr/api/public/cmisVDM.py", line 55, in get_vdm_page
vdm_typeID = vdm_descriptor[1::2]
TypeError: 'NoneType' object is not subscriptable