[Bug/Kindle] Disabled frontlight reset to 0

Hello,

I think I encounter a bug on my Kindle PW4 (FW 5.12.1): if the frontlight is disabled when I exit from KOreader then, when I'm back, the light level is set to 0 so it can't re-enabled it to its previous setting (tap the bottom-left corner always returns "disabled").

Of course, I can live with it, but maybe it's not that hard to fix. :)