Log Message:
Update graphics/giflib to 5.1.2.

Changes:
Version 5.1.2
=============
Code Fixes
----------
* Code hardening using reallocarray() from OpenBSD.
* Sanity check in giffilter catches files with malformed extension records
  Fixes SourceForge bug #63: malformed gif causes segfault in giffilter.
* Inexpensive sanity check in DGifSlurp() catches malformed files with
  no image descriptor. Fixes SourceForge bug #64: malformed gif causes
  crash in giftool.
* Fix SourceForge bug #66: GifDrawBoxedText8x8() modifying constant input
  parameter.
* Bail out of GIF read on invalid pixel width. Addresses Savannah bug
  #67: invalid shift in dgif_lib.c
* Fix SourceForge bug #69: #69 Malformed: Gif file with no extension
  block after a GRAPHICS_EXT_FUNC_CODE extension causes segfault (in
  giftext).
* Fix SourceForge bug #71: Buffer overwrite when giffixing a malformed gif.
* Fix SourceForge bug #73: Null pointer deference in gifclrmap (only
  reachable with malformed GIF).
* Fix SourceForge bug #74: Double free in gifsponge under 5.1,1,
  for any valid gif image.
* Fix SourceForge bug #75: GAGetArgs overflows due to uncounted use of va_arg.
* Sanity check in giffix catches some malformed files. Addresses
  SourceForge bug #77: dgif_lib.c: extension processing error