fix obvious crash

.vscode/launch.json

@@ -0,0 +1,26 @@
+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "Debug Lua Interpreter",
+            "type": "lua-local",
+            "request": "launch",
+            "program": {
+                "lua": "lua",
+                "file": "${file}"
+            }
+        },
+        {
+            "name": "Debug Custom Lua Environment",
+            "type": "lua-local",
+            "request": "launch",
+            "program": {
+                "command": "command"
+            },
+            "args": []
+        }
+    ]
+}

balloon.lua

@@ -311,12 +311,12 @@ function ship.on_step(self, dtime, moveresult)
     end
 
     if pi then
-        if pi.ctrl.up then forward = 1
-        elseif pi.ctrl.down then forward = -1 end
-        if pi.ctrl.jump then climb = 1
-        elseif pi.ctrl.aux1 then climb = -1 end
-        if pi.ctrl.right then right = 1
-        elseif pi.ctrl.left then right = -1 end
+        if pi.up then forward = 1
+        elseif pi.down then forward = -1 end
+        if pi.jump then climb = 1
+        elseif pi.aux1 then climb = -1 end
+        if pi.right then right = 1
+        elseif pi.left then right = -1 end
 
         local yaw = self.object:get_yaw()
         local dir = minetest.yaw_to_dir(yaw)