Fix handling of skipped elements on the very first element transmitted.

Fix handling of skipped elements on the very first element transmitted.
rsync compares e.g. the first mtime against 0, if the mtime is the epoch
then rsync will skip this field and openrsync will choke when receiving it.
So if there is no first element but a FLIST_XYZ_SAME flag is use 0 as
value.
Problem noticed by job@
OK tb@ job@ and yoda@ for fixing the if statements