Fix "Current fanart" not being shown in DialogVideoInfo.

I'm not sure why and I didn't investigate further, but a combination of early
unpacking the fanart and accessing the CFileItemPtr in place of the CFileItem
fixes the issue.

(cherry picked from commit 7f1a748935cbd95f638ba03e4d819d3567d71068)
Merge pull request #5713 from anaconda/fix-curfanart

Fix "Current fanart" not being shown in DialogVideoInfo.