PNG: always strip the existing iCCP chunk

[kmilos]

Otherwise we end up replicating iCCP chunks that have a profile whose name is not "ICC" or "icc" each time when modifying.

$ exiv2 -pS test.png
STRUCTURE OF PNG FILE: test.png
 address | chunk |  length | data                           | checksum
       8 | IHDR  |      13 | ... ...X....                   | 0x15141527
      33 | iCCP  |    8522 | sRGB..h...WT....W...6lr...s.9K | 0x4bde1684
    8567 | tEXt  |   59297 | Raw profile type exif..exif.   | 0x22b5e254
   67876 | IDAT  |    8192 | x^<.[.dKr...}....s....(<P"...R | 0x5dcd61d5
   76080 | IDAT  |    8192 | 2..IgyG..'..^nBN.:.......J.<.u | 0x3c372328
   84284 | IDAT  |    8192 | 01.Y..$>.OXbL..."9.....+UC*... | 0xdc433710
   92488 | IDAT  |    8192 | ....c..(.B...\.k^.i..P..``[..t | 0xf00a7310
   ...

$ exiv2 -M"add Xmp.dc.source XmpText foobar" test.png

$ exiv2 -pS test.png
STRUCTURE OF PNG FILE: test.png
 address | chunk |  length | data                           | checksum
       8 | IHDR  |      13 | ... ...X....                   | 0x15141527
      33 | zTXt  |   17462 | Raw profile type exif..x...k.. | 0xb88d27fa
   17507 | iCCP  |    8522 | sRGB..x...WT....W...6lr...s.9K | 0x65146da4
   26041 | iTXt  |    2407 | XML:com.adobe.xmp.....<?xpacke | 0x4f8f529c
   28460 | iCCP  |    8522 | sRGB..h...WT....W...6lr...s.9K | 0x4bde1684
   36994 | IDAT  |    8192 | x^<.[.dKr...}....s....(<P"...R | 0x5dcd61d5
   45198 | IDAT  |    8192 | 2..IgyG..'..^nBN.:.......J.<.u | 0x3c372328
   53402 | IDAT  |    8192 | 01.Y..$>.OXbL..."9.....+UC*... | 0xdc433710
   61606 | IDAT  |    8192 | ....c..(.B...\.k^.i..P..``[..t | 0xf00a7310
   ...

[codecov]

Codecov Report

Merging #2254 (c2fbff2) into main (7ebf2a1) will decrease coverage by 0.00%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##             main    #2254      +/-   ##
==========================================
- Coverage   63.46%   63.46%   -0.01%     
==========================================
  Files         118      118              
  Lines       19612    19608       -4     
  Branches     9566     9562       -4     
==========================================
- Hits        12447    12444       -3     
  Misses       5096     5096              
+ Partials     2069     2068       -1     

Impacted Files	Coverage Δ
src/pngimage.cpp	59.78% <60.00%> (-0.17%)	⬇️

---

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[kmilos]

After the fix:

$ ./exiv2 -M"add Xmp.dc.source XmpText foobar" test.png

$ ./exiv2 -pS test.png                          
STRUCTURE OF PNG FILE: test.png
 address | chunk |  length | data                           | checksum
       8 | IHDR  |      13 | ... ...X....                   | 0x15141527
      33 | zTXt  |   17462 | Raw profile type exif..x...k.. | 0xb88d27fa
   17507 | iCCP  |    8522 | sRGB..x...WT....W...6lr...s.9K | 0x65146da4
   26041 | iTXt  |    2407 | XML:com.adobe.xmp.....<?xpacke | 0x4f8f529c
   28460 | IDAT  |    8192 | x^<.[.dKr...}....s....(<P"...R | 0x5dcd61d5
   36664 | IDAT  |    8192 | 2..IgyG..'..^nBN.:.......J.<.u | 0x3c372328
   44868 | IDAT  |    8192 | 01.Y..$>.OXbL..."9.....+UC*... | 0xdc433710
   53072 | IDAT  |    8192 | ....c..(.B...\.k^.i..P..``[..t | 0xf00a7310
   ...