Themes: Avoid NPE when setting text in TickerView

It is possible, with the right timing, to receive an NPE in TextSwitcher
when a notification comes in during recreation of the status bar because
of a theme change.

Change-Id: Ia35ad0346f232df905ecff69158b71f3bf61a163
Themes: Fix setting wallpaper from a legacy theme

Change-Id: I3bfc9ee24d2a3ee5c1bdb97f2c07427e6d723206

Conflicts:
	services/java/com/android/server/ThemeService.java