animate nyan makes highlight on buttons broke

[casouri]

When animation is enabled, button highlight is broken. So if I move my cursor (mouse) onto a button, the highlight will show up for like 0.1s, then it's gone, instead of staying highlighted.

I have reproduced this by starting a vanilla Emacs and load nyan-mode.

To reproduce:

• start Emacs with emacs -q
• load nyan-mode
• (nyam-mode)
• (nyan-animate-nyancat)
• M-x customize (there are a lot of buttons in customize homepage)
• move cursor (mouse) to any button and see highlight blink and disappear.

[casouri]

I found that the bug is due to force-mode-line-update.