In Notification.java, ignore ProgressStyle points at start and end.

These are ignored in NotificationProgressBar after ag/31654366. Match
the logic in Notification.java allows more valid points to be drawn.

Flag: android.app.api_rich_ongoing
Fix: 391678201
Test: Post ProgressStyle notifications via test app
Test: patch ag/30006048 and run ProgressStyleNotificationScreenshotTest on device
Test: NotificationProgressBarTest
Change-Id: I04f8d60e10f1c389a8579eb84378636e7a3f5f5b