Fix code issue when SonicV2Connector.get() return None. (sonic-net#13250)

Fix code issue when SonicV2Connector.get() return None.

#### Why I did it
When database key does not exist, SonicV2Connector.get() will return None.
Code will break if not check return value.

#### How I did it
Check SonicV2Connector.get() return value before use it.

#### How to verify it
Pass all E2E test case.

Author: liuh-80

device/alphanetworks/x86_64-alphanetworks_snh60a0_320fv2-r0/plugins/led_control.py

@@ -187,9 +187,15 @@ def _port_name_to_qsfp_index(self, port_name):
         lanes = swss.get(
             swss.APPL_DB, self.PORT_TABLE_PREFIX + port_name, 'lanes')
 
+        # SonicV2Connector.get() will return None when key does not exist.
+        if lanes:
+            lanes_len = len(lanes.split(','))
+        else:
+            lanes_len = 0
+
         # SONiC port nums are 0-based and increment by 4
         # Arista QSFP indices are 1-based and increment by 1
-        return (((sonic_port_num/4) + 1), sonic_port_num % 4, len(lanes.split(',')))
+        return (((sonic_port_num/4) + 1), sonic_port_num % 4, lanes_len)
 
     # Concrete implementation of port_link_state_change() method
 

device/alphanetworks/x86_64-alphanetworks_snh60b0_640f-r0/plugins/led_control.py

@@ -154,9 +154,16 @@ def _port_name_to_qsfp_index(self, port_name):
         lanes = swss.get(
             swss.APPL_DB, self.PORT_TABLE_PREFIX + port_name, 'lanes')
 
+        # SonicV2Connector.get() will return None when key does not exist.
+        if lanes:
+            lanes_len = len(lanes.split(','))
+        else:
+            lanes_len = 0
+
+
         # SONiC port nums are 0-based and increment by 4
         # Arista QSFP indices are 1-based and increment by 1
-        return (((sonic_port_num/4) + 1), sonic_port_num % 4, len(lanes.split(',')))
+        return (((sonic_port_num/4) + 1), sonic_port_num % 4, lanes_len)
 
     # Concrete implementation of port_link_state_change() method