Some FL regression fixes after #4901 (#4921)

* Make hasNaturalLight* caps safe to call without a device check. (fix #4919)
Make it clear that it's expecting the NTX implementation, though.
* Don't turn the FL on on resume if it was off on suspend
* Make sure turnOn/turnOff actually updates hw_intensity in the process where it matters, instead of just in a short lived fork ;). (fix #4923)

frontend/apps/reader/modules/readerfooter.lua

@@ -747,7 +747,7 @@ end
 
 function ReaderFooter:onFrontlightStateChanged()
     if self.settings.frontlight then
-        self:updateFooter()
+        self:updateFooter(true)
     end
 end