app: [Windows] restore double-click restore for custom title bars

Keep custom move areas mapped to HTCAPTION even when the window is
maximized so custom title bars preserve the standard Windows behavior
where double-click restores the window.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/os_windows.go

@@ -494,10 +494,7 @@ func getModifiers() key.Modifiers {
 // hitTest returns the non-client area hit by the point, needed to
 // process WM_NCHITTEST.
 func (w *window) hitTest(x, y int) uintptr {
-	if w.config.Mode != Windowed {
-		// Only windowed mode should allow resizing.
-		return windows.HTCLIENT
-	}
+	if w.config.Mode == Windowed {
 		// Check for resize handle before system actions; otherwise it can be impossible to
 		// resize a custom-decorations window when the system move area is flush with the
 		// edge of the window.
@@ -523,6 +520,7 @@ func (w *window) hitTest(x, y int) uintptr {
 		case right:
 			return windows.HTRIGHT
 		}
+	}
 	p := f32.Pt(float32(x), float32(y))
 	if a, ok := w.w.ActionAt(p); ok && a == system.ActionMove {
 		return windows.HTCAPTION