graphics/ImageMagick: Update to 6.9.6-4

Summarized changelog since 6.9.5-10:

• Off by one memory allocation (reference https://github.com/ImageMagick/ImageMagick/issues/296).
• Prevent fault in MSL interpreter (reference https://www.imagemagick.org/discourse-server/viewtopic.php?f=3&t=30797).
• Added layer ZIP compression to the PSD encoder.
• Unit test pass again after small SUN image patch.
• Fixed incorrect RLE decoding when reading a DCM image that contains multiple segments.
• Fixed incorrect RLE decoding when reading an SGI image (reference https://www.imagemagick.org/discourse-server/viewtopic.php?f=3&t=30514)

PR: 214517
MFH: 2016Q4
Security: CVE-2016-9298