Describe the bug

ICC profile name is stored in a private var profileName_. Its value is set when reading a PNG file but it should also read a value from an ICC profile. Current implementation provides tools to modify ICC profile but makes changing the name of the profile impossible.

To Reproduce

Steps to reproduce the behavior:

1. Load a png without a profile. profileName_ is set to empty.
2. use setICCProfile(), profile data is modified but profileName_ remains empty
3. profile name after the iccp chunk name is exported empty which makes ICC unrecognizable by Chrome, Firefox, Photoshop.
   iCCP�� (69 43 43 50 00 00 in hex ed)
   Line where profileName_ is set

   exiv2/src/pngimage.cpp

   Line 450 in 6e56ec1

   profileName_ = std::string(chunkData.c_str(), iccOffset - 1);

   
   Line where profileName_ is used

   exiv2/src/pngimage.cpp

   Line 613 in 6e56ec1

   outIo.write(reinterpret_cast<const byte*>(profileName_.data()), nameLength) != nameLength ||

Expected behavior

Expecting profileName_ from profile data or at least a method to set a new profileName_