Merge mysql.com:/usr/home/ram/work/bug10798/my50-bug10798

into  mysql.com:/usr/home/ram/work/bug10798/my51-bug10798

sql/slave.cc

@@ -3318,7 +3318,13 @@ static Log_event* next_event(RELAY_LOG_INFO* rli)
         hot_log=0;                              // Using old binary log
       }
     }
-
+    /* 
+      As there is no guarantee that the relay is open (for example, an I/O
+      error during a write by the slave I/O thread may have closed it), we
+      have to test it.
+    */
+    if (!my_b_inited(cur_log))
+      goto err;
 #ifndef DBUG_OFF
     {
       /* This is an assertion which sometimes fails, let's try to track it */