p2p: ifx getting seed nodes for uncommon cases

The code is technically correct, but liable to easily become incorrect with changes

src/p2p/net_node.inl

@@ -799,6 +799,7 @@ namespace nodetool
           "4pixvbejrvihnkxmduo2agsnmc3rrulrqc7s3cbwwrep6h6hrzsibeqd.onion:18083"
         };
       }
+      return {};
     case epee::net_utils::zone::i2p:
       if (m_nettype == cryptonote::MAINNET)
       {
@@ -807,6 +808,7 @@ namespace nodetool
           "sel36x6fibfzujwvt4hf5gxolz6kd3jpvbjqg6o3ud2xtionyl2q.b32.i2p:18080"
         };
       }
+      return {};
     default:
       break;
     }