Fix CTS case testScrollTo.

For 1080p landscape device, the text will be fully displayed without scrolling bar. The text width is less than 1920.
that's, "width - tv.getWidth() - 1" will be a negative value. and tv.getScrollX() will be zero.
And the following assertion failed.
   assertEquals(width - tv.getWidth() - 1, tv.getScrollX());