librsvg regression

USN-4436-1 fixed a vulnerability in librsvg. The upstream fix caused a
regression when parsing certain SVG files. This update backs out the fix
pending further investigation.

Original advisory details:

It was discovered that librsvg incorrectly handled parsing certain SVG
files. A remote attacker could possibly use this issue to cause librsvg to
crash, resulting in a denial of service. This issue only affected Ubuntu
16.04 LTS. (CVE-2017-11464)

It was discovered that librsvg incorrectly handled parsing certain SVG
files with nested patterns. A remote attacker could possibly use this issue
to cause librsvg to consume resources and crash, resulting in a denial of
service. (CVE-2019-20446)