/spreadplayers and /worldborder <center> suggests X/Y instead of X/Z when nothing is typed

Fix of MC-122798 wasn't quite executed properly.

1. Look at a block
2. Type /spreadplayers and a space
3. Observe the second suggestion
   → it shows the X and Y coordinates of the block you're looking at instead of X and Z
4. Type 5
   → it shows the Z coordinate as the new suggestion