Replace RightClickEmpty with RightClickItem.

RightClickEmpty is not fired on the server. RightClickItem fires once
for the same event (a right click in air). This fixes brush and other tools that rely on air
clicks.

worldedit-forge/src/main/java/com/sk89q/worldedit/forge/ForgeWorldEdit.java

@@ -196,7 +196,7 @@ public class ForgeWorldEdit {
             if (we.handleRightClick(player)) {
                 event.setCanceled(true);
             }
-        } else if (event instanceof PlayerInteractEvent.RightClickEmpty) {
+        } else if (event instanceof PlayerInteractEvent.RightClickItem) {
             if (we.handleRightClick(player)) {
                 event.setCanceled(true);
             }