Fix to memory leak leaving WallpaperCropActivity.

After running wallpaper cropper serveral times it crashes with
an OutOfMemotyException.

When leaving WallpaperCropActivity all textures are leaking until end
of process lifetime. This is due to a missing call to function
TiledImageView.destroy which in turn assures TiledImageRenderer
releases held resources.

Resolved by assuring WallpaperCropActivity calls TiledImageView.destroy
from WallpaperCropActivity.onDestroy. In case where onDestroy is not
called resources will be released anyway by process being brought down.

Change-Id: I016b1b9da5f4db8d2b14767edb59fe742415e074
Null pointer exception in FileRotator.java

Sometimes a null pointer exception is thrown when examining files
managed by the file rotator.

The logs from the test show that the Wifi state is changed a large
number of times. On every state change, a write operation is
initiated on the file system. This will eventually result in out
of memory and the call to mBasePath.list() in the maybeRotate(...)
method in FileRotator.java will return null so the iteration will
throw a NullPointerException.

Change-Id: I5d5980d9593bc9ec75281169ca27ee591809903f