package/exiv2: fix CVE-2019-20421

In Jp2Image::readMetadata() in jp2image.cpp in Exiv2 0.27.2, an input
file can result in an infinite loop and hang, with high CPU consumption.
Remote attackers could leverage this vulnerability to cause a denial of
service via a crafted file.

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>