Migration issue for video thumbnails

Between 3.3.x (214c7fc1) and 3.4.0 (312cd83e) of VLC for Android, the db seems to lose some thumbnails.

DB before (3.3.x): vlc_media__14_.db

DB after (3.4.0): vlc_media__15_.db

Logs: logcat__11_.txt

File list: 42.jpg 49.jpg 59.jpg 62.jpg 72.jpg 77.jpg 47.jpg 54.jpg 60.jpg 65.jpg 76.jpg 79.jpg

Media without thumbs:

• RealVideo_RV40_24f_320_240_512K_CookAudio (id: 32)
• Webm_testclip (id: 43)

Reported by @Corbax