This now handles the case where dladdr doesn't return any information
about the filename. This was causing issues on Fuschia.

Bug: chromium:1198567
Change-Id: I892106282fc930d4d26e3eecd720a11e05b8dcd8
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2896171Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>