Fixed another possible crash in the orthogonal renderer

This basically reverts the incomplete 5f6b5cadbd436183a5c530b868d and
fixes the problem a little more reliably.

Starting point only needs to be bound to the first tile of the layer and
ending point only needs to be bound to the last tile. As long as we do
nothing when the starting point ends up beyond the ending point.
Fixed a crash introduced by the repainting fix

tileLayerDrawMarginsChanged should not be emitted for layers that aren't
part of the map for now, since the code handling this signal assumes it
is about a layer of the map.
Merge branch '0.10'