undefined behavior warnings

```
mod_small_light_ext_jpeg.c: In function ‘load_exif_from_memory’:
mod_small_light_ext_jpeg.c:70:58: warning: operation on ‘data’ may be undefined [-Wsequence-point]
mod_small_light_ext_jpeg.c:88:58: warning: operation on ‘data’ may be undefined [-Wsequence-point]
```

In ANSI C, the behavior of the multiple side-effects to a same object(data) in single sentence is undefined.