Fix #34145: 'Save Image' incorrect file type.

Own mistake in 16bit PNG support, wrong bitmask for custom flags

ftype really needs cleanup..

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54369 954f8c5b-7b00-dc11-b283-0030488c597c
fix for [#34133] Creation of an RGBA buffer from an RGB color and an alpha channel not possible.



git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54370 954f8c5b-7b00-dc11-b283-0030488c597c