Fix for bug 6954231 text wraps on second line and is fused...

When breaking a line, the paragraphs below the new line break were still
being drawn in their old location. This only happened when the height
was fill_parent, otherwise the height change would force a relayout,
which in turn would do a full invalidation.

This patch checks for changes to the layout height (not just the widget
height, which won't change when it's fill_parent), and invalidates.

Change-Id: I64adb9f5eae0479c1c9c8d37c10c2c27a6f582a8