demos: cube.cpp - iterating over compositeAlphaFlags
demos: cube.cpp - iterating over compositeAlphaFlags

Error in for loop condition

Change-Id: I8c775f961a6c05dd36e7acfdda6e94399365f90d

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools