table-child: Fix property accessors for spans
table-child: Fix property accessors for spans

Column and row span property accessors would fail if the span wasn't
greater than 1, but 1 is a valid value. Fix the check.

clutter-project/mx,jonnylamb/mx,pwithnall/mx,jonnylamb/mx,pwithnall/mx,clutter-project/mx,pwithnall/mx,jonnylamb/mx,pwithnall/mx,clutter-project/mx,jonnylamb/mx,clutter-project/mx