ReceiveCommits: parseBody before getFooterLines

The RevWalk in ReceiveCommits is used for walking commits in various
places, some of which call parseBody on each commit and some that
don't. The call to RevWalk#getFooterLines on line 1707 was clearly not
preceded by a call to parseBody earlier in the same block; the fact
that it managed to avoid throwing NPE most of the time is pure luck.

We have a report of NPEs in the wild from this line. Make the obvious
fix first, and if we end up having time we can go back and debug later
how it happened.

Change-Id: I5728bb6d46ae4c121c096379b07660f01f86d640

gerrit-server/src/main/java/com/google/gerrit/server/git/ReceiveCommits.java

@@ -1650,6 +1650,7 @@ public class ReceiveCommits {
           break;
         }
         total++;
+        rp.getRevWalk().parseBody(c);
         String name = c.name();
         groupCollector.visit(c);
         Collection<Ref> existingRefs = existing.get(c);