Bug1082555-[Video]-Fix of currentVideo getting reset during suspend resume operation r=russn

I would suggest to use the following:
```
currentVideo = currentVideo | thumbnailList.itemGroups[0].thumbnails[0].data;
```

According to your finding, I try to change the currentVideo even if it has value. This should fix it.

BTW, I may feel that the timing of calling updateLoadingSpinner may be wrong. There are two places to call it:
1. mediadb scanned which will only be called once when app started or sdcard plugged
2. metadata parsing which may be called multiple times

IIRC, I had put a flag to prevent the multiple entries of this function. But I cannot find it now. Maybe, we had removed it or I forgot to do that.