ICC support for Black and White PNG images

Hi there,

After upgrading to Qt 5.14.1 yesterday, my project started throwing the following warnings at startup-time:

qt.gui.icc: Unsupported ICC input color space 47524159
qt.gui.icc: fromIccProfile: failed general sanity check
QPngHandler: Failed to parse ICC profile

Turned out I was using several black-and-white PNG images, which triggered these warnings. After setting the images' mode to RGB the warnings stopped.

They seem to originate from "qtbase/src/gui/painting/qicc.cpp"

I suggest adding support for black-and-white PNG images, or at least recognise them as legit color space (if there is such a thing).

Many thanks,

Holger