Comment # 2 on bug 84179 from Patrick Ohly

I think the "turned off with any value <= 0 seconds" for
SYNCEVOLUTION_PBAP_CHUNK_TRANSFER_TIME comes from a time when
SYNCEVOLUTION_PBAP_CHUNK_MAX_COUNT_[NO_]PHOTO did not exist yet and
_TRANSFER_TIME controlled whether chunking was done at all.

In the current code, setting it to 0 or negative value is invalid (contrary to
what the documentation says). It makes sense to interpret the "turned off" as
"disable auto-tuning" and therefore I am applying the patch to the master
branch.