Try fixing tags with id=0

When tags with the invalid id "0" are encountered in the index.xml file,
KPhotoAlbum now tries to automatically fix them, if possible:

1. If only a single tag in a category has been assigned a zero id, a proper id is assigned.
2. If multiple tags in a category have been assigned a zero id, KPhotoAlbum can not know which tag was originally assigned to the image. In this case, the affected images are tagged with all possible tags plus a marker tag.

CCBUG: 415415