Disable textbox autoscrolling while on screensaver.

If the screensaver gets activated while in a view with autoscrolling textboxes,
on a low powered device like a Raspberry Pi CPU usage can go as high as 80-85%,
the temperature reaches ~71 C (from ~61).

(This also causes CPUFreq governors such as "conservative" or "ondemand" to always
run at the maximum frequency.)

--
This comes from a pull request to popcornmix's experimental branch for the Raspberry Pi. He suggested to send it upstream to make sure scrolling when on screensaver is actually desired.