This version implements the "-reduce" option properly.
This examines the input file to see if the color type,
bit depth,
and palette length can be reduced without loss,
and if there is an opaque alpha channel which can be removed.
Version 1.7.34 introduced a bug in which a file was opened for each trial compression but never written or closed. After a system-dependent number of trials, pngcrush was unable to open a file for the next trial and exited. This release fixes that bug.