DeRichPMTPanel: protect against null test PD pointer

Det/RichDet/src/Lib/DeRichPMTPanel.cpp

@@ -373,10 +373,14 @@ StatusCode DeRichPMTPanel::geometryUpdate() {
         const auto pdID = pd->pdSmartID();
         // test method to get dePD from smartID
         const auto test_pd = dePMT( pdID );
-        if ( test_pd != pd ) {
-          error() << "Inconsistent results from dePMT(RichSmartID)" << endmsg;
-          error() << "   -> requested " << pdID << endmsg;
-          error() << "   -> retrieved " << test_pd->pdSmartID() << endmsg;
+        if ( test_pd ) {
+          if ( test_pd != pd ) {
+            error() << "Inconsistent results from dePMT(RichSmartID)" << endmsg;
+            error() << "   -> requested " << pdID << endmsg;
+            error() << "   -> retrieved " << test_pd->pdSmartID() << endmsg;
+          }
+        } else {
+          error() << "dePMT(RichSmartID) returned NULL PD for " << pdID << endmsg;
         }
       }
     }