Log warning on 'change state corrupt' error

When a 'change state corrupt' error occurs at
least a warning should always be logged so that
a Gerrit administrator has a chance to investigate
this error.

Change-Id: Iebe49f34ea9bc3668bfb7cd96406ae963eeefc85
Signed-off-by: Edwin Kempin <edwin.kempin@gmail.com>

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

@@ -1077,6 +1077,7 @@ public class ReceiveCommits implements PreReceiveHook, PostReceiveHook {
     final PatchSet.Id priorPatchSet = change.currentPatchSetId();
     for (final PatchSet ps : db.patchSets().byChange(request.ontoChange)) {
       if (ps.getRevision() == null) {
+        log.warn("Patch set " + ps.getId() + " has no revision");
         reject(request.cmd, "change state corrupt");
         return null;
       }