Only remove a Window's own entry from the static registry on Dispose

TryRemove(name, out _) deleted whatever instance currently occupied
that key, regardless of identity. If a second Window reused a name
before the first was disposed (Windows[name] = this in the
constructor lets that happen intentionally), disposing the first one
would evict the second, still-live window from the registry even
though it's unaffected. Use the ICollection<KeyValuePair<,>> overload
of Remove, which only deletes the entry when both the key and the
value (reference identity) match.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: shimat

src/OpenCvSharp/Modules/highgui/Window.cs

@@ -80,7 +80,9 @@ public void Dispose()
             return;
         IsDisposed = true;
 
-        Windows.TryRemove(name, out _);
+        // Only remove the map entry if it still points at this instance: another Window may have
+        // since reused the same name (see the constructor), and that instance's entry must survive.
+        ((ICollection<KeyValuePair<string, Window>>) Windows).Remove(new KeyValuePair<string, Window>(name, this));
         trackbars.Clear();
 
         // Destroying the window also releases OpenCV's references to its mouse/trackbar