graphics/ImageMagick7: upgrade to 7.0.11-12 and fix some vulnerabilities

Changelog at https://imagemagick.org/script/changelog.php.

PR: 255802
Approved by: maintainer’s time-out
Security: CVE-2020-27829
Security: CVE-2020-29599
Security: CVE-2021-20176
Security: CVE-2021-20241
Security: CVE-2021-20243
Security: CVE-2021-20244
Security: CVE-2021-20245
Security: CVE-2021-20246