ImageMagick: update to 7.1.0.8.

2021-09-18  7.1.0-8  <quetzlzacatenango@image...>
  * Release ImageMagick version 7.1.0-8 GIT revision 19115:428fe1921:20210918

2021-09-17  7.1.0-8  Dirk Lemstra <dirk@lem.....org>
  * Check for `null` in InvokeDelegate() (reference
    https://github.com/ImageMagick/ImageMagick/issues/4225).

2021-09-12  7.1.0-7  <quetzlzacatenango@image...>
  * Release ImageMagick version 7.1.0-7 GIT revision 19095:d368d3c6b:20210912

2021-09-11  7.1.0-7  Dirk Lemstra <dirk@lem.....org>
  * Fixed incorrect check when module is used as the domain in policy.xml
    that could allow the use of a disabled module. (reference
    https://github.com/ImageMagick/ImageMagick/security/advisories/GHSA-qvhr-jj4p-j2qr).

2021-09-06  7.1.0-7  <quetzlzacatenango@image...>
  * Prevent color reduction merging into one color (reference
    https://github.com/ImageMagick/ImageMagick/issues/4059)

(wiz)