HDFS-4867. metaSave NPEs when there are invalid blocks in repl queue. Contributed by Plamen Jeliazkov and Ravi Prakash.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1490442 13f79535-47bb-0310-9956-ffa450edef68