AddressSanitizer: heap-buffer-overflow on write_png_to_file function

[wcventure]

POC:
POC.zip

Reproduce:
sixel2png $POC

=================================================================
==25754==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60400000054d at pc 0x000000510311 bp 0x7fff615f9850 sp 0x7fff615f9848
READ of size 1 at 0x60400000054d thread T0
    #0 0x510310 in write_png_to_file /home/wencheng/Documents/FuzzingObject/libsixel/src/writer.c:140:22
    #1 0x510310 in sixel_helper_write_image_file /home/wencheng/Documents/FuzzingObject/libsixel/src/writer.c:322
    #2 0x50e373 in sixel_decoder_decode /home/wencheng/Documents/FuzzingObject/libsixel/src/decoder.c:318:14
    #3 0x50c8fc in main /home/wencheng/Documents/FuzzingObject/libsixel/converters/sixel2png.c:226:14
    #4 0x7fb00c79482f in __libc_start_main /build/glibc-LK5gWL/glibc-2.23/csu/../csu/libc-start.c:291
    #5 0x419fa8 in _start (/home/wencheng/Documents/FuzzingObject/libsixel/build/bin/sixel2png+0x419fa8)

Address 0x60400000054d is a wild pointer.
SUMMARY: AddressSanitizer: heap-buffer-overflow /home/wencheng/Documents/FuzzingObject/libsixel/src/writer.c:140:22 in write_png_to_file
Shadow bytes around the buggy address:
  0x0c087fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff8060: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff8070: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff8080: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff8090: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0x0c087fff80a0: fa fa fa fa fa fa fa fa fa[fa]fa fa fa fa fa fa
  0x0c087fff80b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff80c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff80d0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff80e0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff80f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==25754==ABORTING

[saitoha]

Fixed on v1.8.3 with 1377517, Thanks!