Allow LOCAL_ASSET_DIR point to nonexistent dir
Allow LOCAL_ASSET_DIR point to nonexistent dir

LOCAL_ASSET_DIR may point to a dir generated during the build process.
We have done similiar things to LOCAL_RESOURCE_DIR.

Change-Id: Id53433c0d3a4c7af601283755199fde6a59cdfaf

xorware/android_build,xorware/android_build,xorware/android_build,xorware/android_build,xorware/android_build