[MacPorts] #50355: libpng: update to 1.6.21

[MacPorts]

#50355: libpng: update to 1.6.21
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 Reporter:  cal@…   |      Owner:  ryandesign@…
     Type:  update  |     Status:  new
 Priority:  Low     |  Milestone:
Component:  ports   |    Version:  2.3.4
 Keywords:          |       Port:  libpng
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 libpng 1.6.21 is available. Please update to the latest version.

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Ticket URL: <https://trac.macports.org/ticket/50355>
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