dbus: util: add missing try/catch block

Add try/catch block around ObjectMapper call failures.

Change-Id: I5a2a7a8c1049ea16cebe8b87a509bf5104e432ab
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/dbus/dbuspassive.cpp b/dbus/dbuspassive.cpp
index 375960f..c350ea3 100644
--- a/dbus/dbuspassive.cpp
+++ b/dbus/dbuspassive.cpp
@@ -50,6 +50,8 @@
     auto tempBus = sdbusplus::bus::new_default();
     /* service == busname */
     std::string path = GetSensorPath(type, id);
+
+    /* getService can except, should this be in the factory? */
     std::string service = _helper->getService(tempBus, sensorintf, path);
 
     struct SensorProperties settings;