[le audio] Broadcast code parcel fix for zero code length

If broadcast code is empty with 0 length, the code will proceed with serializing with 0 len.
But when deserializing, readByteArray will be ignored if codeLen is zero.
This might cause NullPointerException and concurrent TimeoutException.
The fix is to consider 0 length case.

Bug: 272386069
Test: atest BluetoothLeBroadcastMetadataTest
Test: atest BluetoothLeBroadcastReceiveStateTest
Test: atest BluetoothLeBroadcastSettingsTest

Change-Id: Ide8380efeb21103c56a80cc63a7d355afd4e980e