check if input depth image is 32bit

the program only takes 32bit float depth image
```
      const float* depth_ptr = reinterpret_cast<const float*>(&depth_msg->data[0]);
```

openni2_launch publishes `camera/depth/image` and `camera/depth/image_raw` and `image` is 32FC1, but `mage_raw` is `16UC1`