Fix the show interface counters throwing exception on device with n…

…o external interfaces (sonic-net#2703)

Fix the `show interface counters` throwing exception
issue where device do not have any external ports and all are internal links (ethernet or fabric) which is possible in chassis

scripts/portstat

@@ -333,13 +333,13 @@ class Portstat(object):
                               format_number_with_comma(data['tx_err']),
                               format_number_with_comma(data['tx_drop']),
                               format_number_with_comma(data['tx_ovr'])))
-
-        if use_json:
-            print(table_as_json(table, header))
-        else:
-            print(tabulate(table, header, tablefmt='simple', stralign='right'))
-            if multi_asic.is_multi_asic() or device_info.is_chassis():
-                print("\nReminder: Please execute 'show interface counters -d all' to include internal links\n")
+        if table:
+            if use_json:
+                print(table_as_json(table, header))
+            else:
+                print(tabulate(table, header, tablefmt='simple', stralign='right'))
+        if multi_asic.is_multi_asic() or device_info.is_chassis() and not use_json:
+            print("\nReminder: Please execute 'show interface counters -d all' to include internal links\n")
 
     def cnstat_intf_diff_print(self, cnstat_new_dict, cnstat_old_dict, intf_list):
         """
@@ -551,13 +551,13 @@ class Portstat(object):
                               format_number_with_comma(cntr['tx_err']),
                               format_number_with_comma(cntr['tx_drop']),
                               format_number_with_comma(cntr['tx_ovr'])))
-
-        if use_json:
-            print(table_as_json(table, header))
-        else:
-            print(tabulate(table, header, tablefmt='simple', stralign='right'))
-            if multi_asic.is_multi_asic() or device_info.is_chassis():
-                print("\nReminder: Please execute 'show interface counters -d all' to include internal links\n")
+        if table:
+            if use_json:
+                print(table_as_json(table, header))
+            else:
+                print(tabulate(table, header, tablefmt='simple', stralign='right'))
+        if multi_asic.is_multi_asic() or device_info.is_chassis() and not use_json:
+            print("\nReminder: Please execute 'show interface counters -d all' to include internal links\n")
 
 def main():
     parser  = argparse.ArgumentParser(description='Display the ports state and counters',