graphics/ImageMagick6: Update to 6.9.9.38.

6.9.9-38
- Fixed numerous use of uninitialized values, integer overflow, memory
  exceeded, and timeouts

6.9.9-37
- Fixed numerous use of uninitialized values, integer overflow, memory
  exceeded, and timeouts

6.9.9-36
- Do not refer to page in OptimizeLayerFrames
- PerlMagick unit tests pass again.
- Fixed numerous use of uninitialized values, integer overflow, memory
  exceeded, and timeouts

6.9.9-35
- Add support for reading the HEIC image format to the Windows build.
- Fixed numerous use of uninitialized values, integer overflow, memory
  exceeded, and timeouts
- Add list-length policy to limit the maximum image sequence length.

6.9.9-34
- Support aspect ratio geometry, e.g. -crop 3:2.
- Add support for reading the HEIC image format
- Fix IM build when HEIC is enabled.
- Fixed numerous memory leaks, credit to OSS Fuzz.

6.9.9-33
- Fix some enum values in the OpenCL code.

6.9.9-32
- Fixed numerous memory leaks

6.9.9-31
- Check for webpmux library version 0.4.4

6.9.9-30
- Fix error reading from pipe under Windows

6.9.9-29
- Fix heap use after free error

6.9.9-28
- Fix error reading multi-layer XCF image file.
- Fix possible stack overflow in WEBP reader
- Fixed numerous memory leaks

6.9.9-27
- Overall standard deviation is the average of each pixel channel

6.9.9-26
- Support Stereo composite operator.
- Fix build failure with --without-modules

6.9.9-25
- Fix build failure with libraw 0.14.8

6.9.9-24
- Support HDRI color profile management.
- Don't delete in-memory blob when reading an image

6.9.9-23
- Fixed initialization of OpenCL

6.9.9-22
- Fixed a problem with resource bookkeeping in AcquireMatrixInfo().

6.9.9-21
- Encode JSON control characters

(fhajny)