Fix specified wallpaper color option missing after reboot

Not only check latest wallpaper type (FLAG_SYSTEM, FLAG_LOCK) but also
check if the wallpaper color is specified to determine if we reset the
theme overlay setting.

Bug: 198449419
Test: atest ThemeOverlayControllerTest
Change-Id: Ic10c10c6fbccee0f330c67ae8b9bacb947c5e035