cocoa-cb: fix title bar button state on start up

on start up it was possible to click the hidden buttons. hide the
buttons ons tart up to make the state consistent with the visible state.

video/out/cocoa-cb/title_bar.swift

@@ -55,6 +55,8 @@ class TitleBar: NSVisualEffectView {
                            frame.size.width, TitleBar.height)
         cocoaCB = ccb
         super.init(frame: f)
+        buttons.forEach { $0.isHidden = true }
+        isHidden = true
         alphaValue = 0
         blendingMode = .withinWindow
         autoresizingMask = [.width, .minYMargin]