Ensure prior commit body is parsed before comparing messages

Otherwise we NPE when we try to replace a patch.

Change-Id: Ia49c62e00aa4f8784a7e8f488059e48914801b92
Signed-off-by: Shawn O. Pearce <sop@google.com>
diff --git a/src/main/java/com/google/gerrit/server/ssh/commands/Receive.java b/src/main/java/com/google/gerrit/server/ssh/commands/Receive.java
index e8c38de..a0ebb16 100644
--- a/src/main/java/com/google/gerrit/server/ssh/commands/Receive.java
+++ b/src/main/java/com/google/gerrit/server/ssh/commands/Receive.java
@@ -990,6 +990,7 @@
             //
             if (priorPatchSet.equals(ps.getId())
                 && c.getTree() == prior.getTree()) {
+              rp.getRevWalk().parseBody(prior);
               if (c.getFullMessage().equals(prior.getFullMessage())) {
                 reject(request.cmd, "no changes made");
                 return null;