Further work on flicker reduction

Further work on flicker reduction

This sort of reverts 67fb95f49ef2cbc88e3042bcac50760cf5bf797f. Sadly
that commit didn't provide too much information on the exact problem
it was trying to solve.

Reverting it reduces flicker for, at least:
xdotool search -class llpp key --delay 100 --repeat 100 ctrl+plus ctrl+minus

Cause of flicker:

Reshape implied
  geometry call
  invalidate ~redisplay:true
    state.layout <- []
    state.redisplay <- true

Next time display is called the layout is not yet ready so it has but
one option - to paint the whole visible area with the background
color.

Later when geometry processing/layouting/rendering is complete another
redisplay will be schedulled and correct things will be drawn, but due
to the fill with default background color done previously (when
state.layout was empty) screen will flicker.