Avoid overflow when calculating ptr address for 3D textures in RenderingDevice texture update

[clayjohn]

Fixes: #74173

image_size * z could easily overflow with 3D textures even at modest sizes. For 2D textures z is always 0 so this never overflowed. This bug essentially breaks all 3D textures with a size larger than 256x256x256 with FORMAT_L8.

In the linked issue image size was 33,554,432 (W x H x D x 1bit) since all values were uint32_ts this caused the calculation to overflow whenever z was a multiple of 64. With higher bit depths the overflow happens more frequently. Since z / depth is always less than one and image_size is always a multiple of depth we can swap the order of operations to keep the values within a manageable range.

[akien-mga]

Thanks!

[YuriSizov]

Cherry-picked for 4.0.1.