Fix missing .fsv_sig after partial split install

Test: adb install-multiple foo.apk foo.apk.fsv_sig
      adb install-multiple -p com.foo foo_split.apk foo_split.apk.fsv_sig
      # See base.apk.fsv_sig in /data/app/com.foo-*/
Bug: 112037636
Change-Id: I043c7bf545164c58b2cc37507d10188c25033f6b