Bug#1014125: libheif: CVE-2020-23109

[Bastian Germann]

Control: fixed -1 1.8.0-1

This is claimed to be fixed with 
https://github.com/strukturag/libheif/commit/bca0162018df9a32d21c05aad1fa203881fa7813
which was included in v1.7.0