Fix zombie window leak by passing win pointer directly to finish_destroy_win

[jEsuSdA]

Summary

Fixes a memory leak where destroyed windows accumulate indefinitely because finish_destroy_win() cannot find them via ID lookup.

Problem

finish_destroy_win() searched for the window by ID using a linear scan that required w->destroyed == True. However, find_win() (used by destroy_win() and other callers) filters out destroyed windows:

win* find_win(Window id) {
  for (w = list; w; w = w->next) {
    if (w->id == id && !w->destroyed)  // <-- filters out destroyed!
      return w;
  }
}

When destroy_win() marks a window as destroyed and then calls finish_destroy_win(), the latter scans the list looking for w->destroyed == True. But if find_win() was called in between (or if the window is accessed again), the destroyed window is skipped. More importantly, finish_destroy_win() itself searches by ID and requires w->destroyed, but since the caller already has the win* pointer, the search is redundant and fragile.

The result: zombie win structs accumulate in the window list forever, causing memory growth and eventual slowdown over long sessions.

Solution

Change finish_destroy_win() to accept a win* pointer directly instead of a Window ID. The callers already have the pointer:

• destroy_win() finds it via find_win() before marking destroyed
• destroy_callback() receives it as an argument

This eliminates the problematic ID lookup entirely.

Scope

• Only fastcompmgr.c is touched
• Function signature change + two caller updates
• make clean && make produces zero warnings, zero errors

Note

The list unlink logic remains a linear scan (to be replaced by O(1) unlink once the doubly-linked list PR is merged).