always release data_lock mutex to avoid deadlock

Summary: in stage-1 replicaset, when kill a secondary instance, sometime the instance will run into deadlock due to process_raft_queue thread forgot to release its acquired mutex in raft_change_master

Reviewed By: Pushapgl, bhatvinay

Differential Revision: D27602667

sql/rpl_replica.cc

@@ -1796,7 +1796,10 @@ int raft_change_master(
   channel_map.rdlock();
   Master_info *mi = channel_map.get_default_channel_mi();
 
-  if (!mi) goto end;
+  if (!mi) {
+    channel_map.unlock();
+    DBUG_RETURN(error);
+  }
 
   mysql_mutex_lock(&mi->data_lock);
   strmake(mi->host, const_cast<char *>(master_instance.first.c_str()),
@@ -1826,12 +1829,12 @@ int raft_change_master(
   }
   mi->inited = true;
   mi->flush_info(true);
-  mysql_mutex_unlock(&mi->rli->data_lock);
-  mysql_mutex_unlock(&mi->data_lock);
 
   // changing to a slave. set the is_slave flag
   is_slave = true;
 end:
+  mysql_mutex_unlock(&mi->rli->data_lock);
+  mysql_mutex_unlock(&mi->data_lock);
   channel_map.unlock();
   DBUG_RETURN(error);
 }