fixed 'load table from master' hang when host is empty

added respective test case

mysql-test/r/rpl_empty_master_crash.result

+Master_Host	Master_User	Master_Port	Connect_retry	Log_File	Pos	Slave_Running	Replicate_do_db	Replicate_ignore_db	Last_errno	Last_error	Skip_counter
+		0	0		0	No			0		0

mysql-test/t/rpl_empty_master_crash.test

+source include/master-slave.inc;
+connection master;
+use test;
+drop table if exists t1;
+show slave status;
+#--error 1218 # for mysql-4.0
+--error 1042
+load table t1 from master;

sql/slave.cc

@@ -451,6 +451,12 @@ int fetch_nx_table(THD* thd, MASTER_INFO* mi)
     goto err;
   }
 
+  if (!mi->host || !*mi->host)
+  {
+    nx_errno = ER_BAD_HOST_ERROR;
+    goto err;
+  }
+
   safe_connect(thd, mysql, mi);
   if (slave_killed(thd))
     goto err;