FIX: do not parse dirty json info

Change-Id: I543ae2818c5b23c351dc355abf115e76d5af75dc

src/slic3r/GUI/DeviceManager.cpp

@@ -2032,6 +2032,7 @@ int MachineObject::parse_json(std::string payload)
                                     });
                                     return -1;
                                 }
+                                return -1;
                             }
                         } else {
                             BOOST_LOG_TRIVIAL(warning) << "unsupported msg_type=" << j_pre["print"]["msg"].get<std::string>();