ANDROID: sdcardfs: Check for private data earlier

When an sdcardfs dentry is destroyed, it may not yet
have its fsdata initialized. It must be checked before
we try to access the paths in its private data.

Additionally, when cleaning up the superblock after
a failure, we don't have our sb private data, so
check for that case.

Bug: 77923821
Change-Id: I89caf6e121ed86480b42024664453fe0031bbcf3
Signed-off-by: Daniel Rosenberg <drosen@google.com>
Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org>