graphics/pngcrush: 1.7.86 -> 1.7.87

• Fixed a double-free bug. There was a "free" of the sPLT chunk structure in pngcrush and then again in png.c (Bug report by Brian Carpenter).
• Added common-law trademark notice and export control information.
• Rearranged some paragraphs in the comments at the beginning of pngcrush.c
• Increased some buffer sizes in an attempt to prevent possible overflows.

PR: 204421
Submitted by: Anton Sayetsky <vsasjason@gmail.com> (maintainer)