Clean up Joystick parent-child on red-X dismissal

JoystickConfigurationController previously did its parent-child
teardown in -cancel:, leaving the red-X dismissal path (and the
Preferences-close cascade) without a removeChildWindow:. The stale
relationship was reconciled on the next showWindow: by the parent
check, so the bug was invisible in practice — but the asymmetry
diverged from the close-path matrix in spec 004 which mandates a
single teardown hook for every closable-with-pause-or-parent panel.

Add an NSWindowWillCloseNotification observer in showWindow:; route
the unpin through handleWillClose: so every dismissal path (Apply,
Cancel, red X, Preferences close cascade) does the same teardown.

Joystick is the only utility window whose showWindow: can run a
second time without an intervening close: re-clicking Configure for
the other joystick reuses the same instance, switching contents via
sender's tag. The spec explicitly disallows a singleton early-return
guard here. To keep observer registration idempotent across that
switch, remove any prior registration before adding.

Author: morozov

fusepb/controllers/JoystickConfigurationController.m

@@ -154,10 +154,24 @@ - (IBAction)apply:(id)sender;
 
 - (IBAction)cancel:(id)sender
 {
-  [[self window] unpinFromParent];
+  /* All dismissal paths (Apply, Cancel, red X, Preferences close
+     cascade) funnel through handleWillClose: via the
+     NSWindowWillCloseNotification observer registered in showWindow:,
+     so this just closes the window and lets the observer do the
+     parent-child teardown. */
   [[self window] close];
 }
 
+- (void)handleWillClose:(NSNotification *)note
+{
+  [[NSNotificationCenter defaultCenter]
+    removeObserver:self
+              name:@"NSWindowWillCloseNotification"
+            object:[self window]];
+
+  [[self window] unpinFromParent];
+}
+
 - (void)showWindow:(id)sender
 {
   size_t i;
@@ -176,6 +190,20 @@ - (void)showWindow:(id)sender
      enforces z-order for two windows at the same level. */
   [[self window] pinAsChildOf:parent];
 
+  /* Register the close observer here. Joystick is reused across Joy1
+     and Joy2 invocations on the same open window (the spec disallows a
+     singleton early-return guard for that reason), so showWindow: may
+     run a second time without an intervening close — remove any prior
+     registration before adding to keep this idempotent. */
+  NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
+  [nc removeObserver:self
+                name:@"NSWindowWillCloseNotification"
+              object:[self window]];
+  [nc addObserver:self
+        selector:@selector(handleWillClose:)
+            name:@"NSWindowWillCloseNotification"
+          object:[self window]];
+
   [joyXAxis removeAllItems];
   [joyYAxis removeAllItems];