processor: fix uniqueID to return error instead of infinite loop on Stat errors

Previously, uniqueID(postsDir, t) returned only a string and looped
forever when os.Stat returned an error other than IsNotExist
(e.g. permission denied). Change the signature to (string, error),
propagate the error, and update the caller in processFile to handle
it. Add positive and negative tests covering new ID generation,
suffix collision, and permission-based stat failure.

0 files changed, 0 insertions, 0 deletions