Fix RRO when LOCAL_EXPORT_PACKAGE_RESOURCES is unset

If LOCAL_EXPORT_PACKAGE_RESOURCES is unset then
append_enforce_rro_sources was inserting a blank entry into
the 4th.  When converting the || separator back to space that
resulted in a two sequential spaces, which is treated as a
single word separator, causing the 5th field to be treated
as the 4th field.

Put "false" into the 4th field in soong_app_prebuilt.mk to match
package_internal.mk.

Bug: 123510624
Test: m SystemUIGoogle
Change-Id: I794c413e33df2020d0dc43379cfb017e7e09baa1