Crash navigating into multimeasure rest using Measure Properties

6e47f74, Ubuntu 14.04

1) enter some notes into measures 1 & 4, leaving 2 & 3 empty (other measures can contain whatever)
2) enable mmrests
3) save
4) close
5) reload
6) measure 1, measure properties
7) use arrow buttons to navigate to measure 2

Result: crash, as measure 2 has no "system" - it has not been laid out on its own, since it was alreayd part of an mmrest when the score was loaded. Crash happens trying to draw the selection rectangle.

I would propose catching the case where the start or end point of the select is within an mmrest and doing something reasonable. I am not so sure we do something reasonable even if the measure *has* been laid out. Try My First Score, enter notes in first & last measure, enable mmrests, and try to navigate in measure proerties. Selection rectangle follows the original local of the underlying measures. Maybe better would be draw a dashed rectanlge around the whole mmrest?

where system or system2 is null and doing something reasonable. Maybe check to see if we're in an mmrest (the most likely case) and drawing the rectangle around the whole rest.