Workaround for firstResponder NSPopover bug

NSPopoverDelegateResponderFix.m

- (void)popoverWillClose:(NSNotification *)notification
{
    // https://openradar.appspot.com/26064913
    // Turns out that Apple has a bug in their responder chain. It stores a non-weak (assign)
    // "_previousResponder", which is a button inside the deallocated popover. During window
    // state restoration/archiving, it tries to access this object (the button) and crashes.
    // We work around this by resetting the "_previousResponder" when the popover closes.
    NSResponder *firstResponder = [[[self view] window] firstResponder];
    [[[self view] window] makeFirstResponder:nil];
    
    if ([[[_popover contentViewController] view] window] == firstResponder) {
        return;
    }
    
    if ([firstResponder isKindOfClass:[NSView class]]) {
        NSView *responderView = (NSView *)firstResponder;
        while (responderView) {
            if ([responderView superview] == [[_popover contentViewController] view]) {
                return;
            }
            responderView = [responderView superview];
        }
    }
    [[[self view] window] makeFirstResponder:firstResponder];
}