PNG with ICC Profile breaks cache on x64

[GhostlyDark]

What's broken:
Certain PNG files cause a crash when trying to generate cache. It turns out that image files with a certain profile are causing this. ImageMagick puts this out:
iCCP: profile 'ICC Profile': 'GRAY': Gray color space not permitted on RGB PNG

Affected platforms:
This only happens with Project 64 (64-bit) and mupen64plus (64-bit) as this is not reproducable with their 32-bit counterparts. Tested on Windows 10 1903 x64.

Workaround:
Stripping the image or reexporting with GIMP fixes this.
Using GLideN64's 32-bit version instead works as well.

Reproduce:
ImageMagick Full Output
Test Images

[gonetz]

Fixed with 4b263e3
I tested mupen64plus x64 only.
The fix included into latest WIP build, #2037

The problem was really with that profile. pnglib tried to output into stderr the same warning about Gray color space, but console output crashes for some reason with x64 build, so I just disabled it.

[GhostlyDark]

Grabbed the x64 mupen build from AppVeyor since the WIP build is a few hours too old.
I can confirm that it is fixed. Thank you again!