Fix out_of_range error in System_utils_posix 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/+/2896171 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>