fix memory leak when swallowing windows

include/window.h

@@ -9,6 +9,12 @@
  */
 #pragma once
 
+/**
+ * Frees an i3Window and all its members.
+ *
+ */
+void window_free(i3Window *win);
+
 /**
  * Updates the WM_CLASS (consisting of the class and instance) for the
  * given window.

src/manage.c

@@ -310,6 +310,9 @@ void manage_window(xcb_window_t window, xcb_get_window_attributes_cookie_t cooki
             }
         }
     }
+    if (nc->window != cwindow && nc->window != NULL) {
+        window_free(nc->window);
+    }
     nc->window = cwindow;
     x_reinit(nc);
 

src/tree.c

@@ -266,11 +266,8 @@ bool tree_close_internal(Con *con, kill_window_t kill_window, bool dont_kill_par
             add_ignore_event(cookie.sequence, 0);
         }
         ipc_send_window_event("close", con);
-        FREE(con->window->class_class);
-        FREE(con->window->class_instance);
-        i3string_free(con->window->name);
-        FREE(con->window->ran_assignments);
-        FREE(con->window);
+        window_free(con->window);
+        con->window = NULL;
     }
 
     Con *ws = con_get_workspace(con);

src/window.c

@@ -11,6 +11,18 @@
  */
 #include "all.h"
 
+/*
+ * Frees an i3Window and all its members.
+ *
+ */
+void window_free(i3Window *win) {
+    FREE(win->class_class);
+    FREE(win->class_instance);
+    i3string_free(win->name);
+    FREE(win->ran_assignments);
+    FREE(win);
+}
+
 /*
  * Updates the WM_CLASS (consisting of the class and instance) for the
  * given window.