Warn about invalid //stretch usage

ChatCommands.md

@@ -289,9 +289,9 @@ Stack the current WorldEdit region `<count>` times by offset `<x>`, `<y>`, `<z>`
 
 Scale the current WorldEdit positions and region by a factor of `<stretchx>`, `<stretchy>`, `<stretchz>` along the X, Y, and Z axes, repectively, with position 1 as the origin.
 
-    //scale 2 2 2
-    //scale 1 2 1
-    //scale 10 20 1
+    //stretch 2 2 2
+    //stretch 1 2 1
+    //stretch 10 20 1
 
 ### `//transpose x/y/z/? x/y/z/?`
 

worldedit_commands/init.lua

@@ -905,9 +905,12 @@ minetest.register_chatcommand("/stretch", {
 		stretchx, stretchy, stretchz = tonumber(stretchx), tonumber(stretchy), tonumber(stretchz)
 		if stretchx == 0 or stretchy == 0 or stretchz == 0 then
 			worldedit.player_notify(name, "invalid scaling factors: " .. param)
+			return nil
 		end
 		local count = check_region(name, param)
-		if count then return tonumber(stretchx) * tonumber(stretchy) * tonumber(stretchz) * count end
+		if count then
+			return stretchx * stretchy * stretchz * count
+		end
 		return nil
 	end),
 })