Folder broken after being unindexed

When a folder is indexed after it was previously unindexed, ML does not return it, because nb_video = 0.

Steps to reproduce :

index a folder 'Download' with one video => folder.nb_video=1 (vlc_media_1.db)
unindex 'Download' folder => folder row is removed or folder.nb_video=0 (i've seen both), media is converted to external (vlc_media_2.db)
index the folder again => folder.nb_video=0, even if the media is converted back to normal and linked to that folder (vlc_media_3.db)

in vlc-android, the video is invisible with "Group videos by folder", while being visible with "Group videos by name" or without grouping.

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