Fix crash in SensorService. Ignore devices with no sensors.

Change-Id: I1491740baa6348f97c336b6883b11ad2ab93cf73
diff --git a/services/sensorservice/SensorService.cpp b/services/sensorservice/SensorService.cpp
index cf750ee..f6ff092 100644
--- a/services/sensorservice/SensorService.cpp
+++ b/services/sensorservice/SensorService.cpp
@@ -271,6 +271,8 @@
                 dev.enableAllSensors();
             }
             return status_t(NO_ERROR);
+        } else if (mSensorList.size() == 0) {
+            result.append("No Sensors on the device\n");
         } else {
             // Default dump the sensor list and debugging information.
             result.append("Sensor List:\n");