bundle2: seek part back during iteration Previously, iterparts would yield the part to users, then consume the part. This changed the part after the user was given it and left it at the end, both of which seem unexpected. Let's seek back to the beginning after we've consumed it. I tried not seeking to the end at all, but that seems important for the overall bundle2 consumption. This is used in a future patch to let us move the bundlerepo bundle2-changegroup-part to be handled entirely within the for loop, instead of having to do a seek back to 0 after the entire loop finishes. Differential Revision: https://phab.mercurial-scm.org/D289