sfpshow: prevent 'show int trans eeprom --dom' from crashing (sonic-n…

…et#567)

When some specific 25G DAC attached to the system, the 'dom_info_dict'
could be a None object, as a result, the 'show int transceiver eeprom --dom'
will crash.

And thus, in this commit, we'll add an additional checker for the None object.

Signed-off-by: Dante (Kuo-Jung) Su <dante.su@broadcom.com>
Change-Id: Ic2b5eb38ddf98b98cce7eddf161595013a19c720

scripts/sfpshow

@@ -75,7 +75,7 @@ class SFPShow(object):
         out_put=''
         ident = '        '
         for key in sorted_key_table:
-            if dom_info_dict[key] != 'N/A':
+            if dom_info_dict is not None and dom_info_dict[key] != 'N/A':
                 if dom_info_dict[key] == 'Unknown':
                     out_put = out_put + ident + ident + channel_monitor_map[key] + ': ' + dom_info_dict[key] + '\n'
                 else: