frameworks/base: Fix wallpaper preview surface destroy call

When we start wallpaper preview and before wallpaper preview
is shown, it gets hidden due to another app and then preview
surface gets destroyed. Renderscript is not aware of this
and it gets out-of-sync and we see egl error messages.

Change-Id: I75faff4dfbe16256ed688088cf0639ecf8cb158e
CRs-Fixed: 231711,231091,230739