vold: fix crash for non-emulated primary storage

When EMULATED_STORAGE_SOURCE is not set, emulated_source
will be null

Change-Id: I22d040eda498d4c2a5becd367eb5b9a55a494e0b
vold: restore 4.4 sdcard logic

Mount points in 4.4 are always fuse-wrapped to provide granular
permission. Unix file systems no longer need to be manually
fuse-wrapped by us.

Change-Id: I6885b0baeaae7c380ec32d410a70a4f53801157b