Fix broken progress bar rendering.

Commit 1b090f777301ff57d8bfb83b6d251edaea53b0b9 made the progress bar
being drawn incorrectly, because it made the empty part of the progress
bar always being drawn completely, even though it should be drawn only
partly, because there's also a filled part. Fixit.

Change-Id: I3d574d1ab3dc0a7c8f85c90a03f084caf852de0d