Fix a typo in wxWindow::CaptureMouse() comment

There are no functional changes.

Closes https://github.com/wxWidgets/wxWidgets/pull/1291

include/wx/window.h

@@ -1019,7 +1019,7 @@ public:
 
         // start or end mouse capture, these functions maintain the stack of
         // windows having captured the mouse and after calling ReleaseMouse()
-        // the mouse is not released but returns to the window which had had
+        // the mouse is not released but returns to the window which had
         // captured it previously (if any)
     void CaptureMouse();
     void ReleaseMouse();