Handle unexpected cases in profile saver

There are some unexpected cases that should not occur in a normal run.
Log warnings but avoid crashing if:
- dex location is empty
- we cannot figure the real paths of the locations.

Bug: 27532729

(cherry picked from commit 1fae45f7)

Change-Id: I9e8f4fc2da49f47dab113795ac264c6db9b691de