[surepetcare] Fix NPE (#16088)

Signed-off-by: Jacob Laursen <jacob-github@vindvejr.dk>

bundles/org.openhab.binding.surepetcare/src/main/java/org/openhab/binding/surepetcare/internal/discovery/SurePetcareDiscoveryService.java

@@ -89,6 +89,7 @@ public class SurePetcareDiscoveryService extends AbstractDiscoveryService
     @Override
     public void setThingHandler(@Nullable ThingHandler handler) {
         if (handler instanceof SurePetcareBridgeHandler bridgeHandler) {
+            this.bridgeHandler = bridgeHandler;
             bridgeUID = bridgeHandler.getUID();
         }
     }