fix related to http status code in 'getDevices' endpoint

components/device-mgt/org.wso2.carbon.device.mgt.api/src/main/java/org/wso2/carbon/device/mgt/jaxrs/service/impl/DeviceManagementServiceImpl.java

@@ -127,7 +127,8 @@ public class DeviceManagementServiceImpl implements DeviceManagementService {
                 }
             } else {
                 result = dms.getAllDevices(request);
-                if (result == null) {
+                int resultCount = result.getRecordsTotal();
+                if (resultCount == 0) {
                     throw new NotFoundException(
                             new ErrorResponse.ErrorResponseBuilder().setCode(404l).setMessage("No device is currently" +
                                     " enrolled with the server").build());