ok op, tracey

ok stsp@

reported by jrick and op@ ok op@

otherwise some fields may be unitialized and fail the validation done on the receiving side. ok stsp@

The old code did not work correctly if only a single object Id was to be sent to got-read-pack. Make got-read-pack error out if the list of commits for object enumeration is empty to catch this problem if it occurs again. Found by the send_basic test, which was failing with GOT_TEST_PACK=1 ok tracey

This allows the main process to avoid looping over all object IDs again in case the pack file used for enumeration is complete. ok op@

in this case they're luckily the same; got_imsg_object_idlist and got_imsg_reused_delta only have one size_t long field. ok stsp@

use correct error code and ok stsp@

Simplifies the reading of the author/committer string and makes also the code shorter. ok stsp@

recv_imsg_error already checks the size of the message, and it does so more precisely than the removed code. ok stsp@

The problem that was found in the earlier version has been fixed. ok op@