After some detective work I have been able to get XnView to work with ghostscript again. I am not sure when it broke but I have a fix for it.
It appears that two of the environment variables inside of XnView were changed as follows.
GS_DLL -> XNVIEW_GS_DLL
GS_LIB -> XNVIEW_GS_LIB
As a result the [Environment] entries in XnViewPortable.ini located in the App\AppInfo\Launcher\ directory need to be changed to reflect this. The new entries should be:
[Environment]
XNVIEW_GS_DLL=%CustomGSDirectory%\bin\gsdll32.dll
XNVIEW_GS_LIB=%CustomGSDirectory%\bin;%CustomGSDirectory%\lib;%CustomGSDirectory%\fonts
If a developer could make this change in the distribution package, so that future upgrades do not break it again, it would be much appreciated.
This was fixed in the XnView Portable 2.32 release
Sometimes, the impossible can become possible, if you're awesome!