when returning with an error.

the unknown-sAPI test is failing.

and png_set_eXIf_1(), respectively, to avoid breaking API compatibility
with libpng-1.6.31.

  in pngwrite.c, and made various other fixes to png_write_eXIf().
Eliminated png_ptr->num_exif member from pngstruct.h and added num_exif
  to arguments for png_get_eXIf() and png_set_eXIf().

are allowed. Avoid leaking the input buffer "eXIf_buf".

(Bug report by John Smith)

tags) to pngtest.png.

  result when integers appear on both sides of a compare.  Worked around the
  others by forcing the strict-overflow setting in the relevant functions to
  a level where they are not reported.
Changed "FALL THROUGH" comments to "FALLTHROUGH" because GCC doesn't like
  the space.
Worked around some C-style casts from (void*) because g++ 5.4.0 objects
  to them.
Increased the buffer size for 'sprint' to pass the gcc 7.1.0 'sprint
  overflow' check that is on by default with -Wall -Wextra.

enabled.

possible integer overflow (Bug report by John Bowler).