vold: Avoid SIGSEGVs when fstab lacks /data

This change adds null-checks for all the places where cryptfs tries to
access the /data entry in fstab, to avoid crashes.

Bug: 80493321
Test: No crashes in Android-in-Chrome OS (which lacks /data in fstab)
Change-Id: Id6cdfe01cdd336cebf8afb9bdd07135811115182
Merged-In: Id6cdfe01cdd336cebf8afb9bdd07135811115182
1 file changed