Fix incorrect index calculations in image conversions (#735) #176

Job	Run time
windows (windows-latest, v143, x64, Debug,Release, ON, ON, OpenGL+Vulkan, ON, ON, ON, YES, ON, OFF)	27m 25s
windows (windows-latest, v143, x64, Release, OFF, OFF, OFF, OFF, OFF, NO, OFF, OFF)	2m 4s
windows (windows-latest, v143, x64, Release, OFF, OFF, OFF, OFF, OFF, NO, OFF, ON)	2m 45s
windows (windows-latest, v143, x64, Release, OFF, OFF, OFF, OFF, OFF, NO, ON, ON)	5m 50s
windows (windows-latest, CLangCL, x64, Debug,Release, ON, ON, OpenGL+Vulkan, ON, ON, ON, YES, ON,...	35m 47s
windows (windows-latest, CLangCL, x64, Release, OFF, OFF, OFF, OFF, OFF, NO, OFF, OFF)	4m 1s
windows (windows-latest, CLangCL, x64, Release, OFF, OFF, OFF, OFF, OFF, NO, OFF, ON)	7m 10s
windows (windows-latest, CLangCL, x64, Release, OFF, OFF, OFF, OFF, OFF, NO, ON, ON)	6m 36s
windows (windows-2019, v142, x64, Debug,Release, ON, ON, OpenGL+Vulkan, ON, ON, ON, NO, ON, OFF, ...	24m 12s
windows (windows-latest, CLangCL, arm64, Debug,Release, ON, ON, OFF, ON, ON, ON, YES, Visual Stud...	19m 17s
	2h 15m 7s

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