This seems to be the default value when the vertex attribute is disabled, or components aren't defined. This fixes a regression from #2307 in SMO where a plant in the Wooded Kingdom would draw slightly differently in the depth prepass, leading to depth test failing later on. GDK has stated that the specific case in Gundam only expects x and y to be 0, and Vulkan's undefined value for z does appear to be 0 when a vertex attribute type does not have that component, hence the value (0, 0, 0, 1). This worked in Vulkan despite also providing an all 0s attribute due to the vertex attribute binding being R32Float, so the other values were undefined. It should be changed there separately.