Properly send the reply in clearWallpaperComponentLocked

This fixes an error in ag/24482229, causing the callback not to be sent
in the case a clear is triggered because the wallpaper package does not
exist on the device anymore.

Bug: 273443374
Test: atest WallpaperManagerTest
Change-Id: Iafba8ac7dfbc2d85f45118a6ac4ff75b64bb5b85