cleanup: redundant my_casedn_str()

hashing/comparison uses case-insensitive collation anyway

mysql-test/suite/rpl/r/rpl_master_pos_wait.result

@@ -43,6 +43,9 @@ NULL
 select master_pos_wait('master-bin.000001',1000000,1,"my_slave");
 master_pos_wait('master-bin.000001',1000000,1,"my_slave")
 -1
+select master_pos_wait('master-bin.000001',1000000,1,"MY_SLAVE");
+master_pos_wait('master-bin.000001',1000000,1,"MY_SLAVE")
+-1
 STOP SLAVE 'my_slave';
 RESET SLAVE 'my_slave' ALL;
 change master to master_port=MASTER_MYPORT, master_host='127.0.0.1', master_user='root';

mysql-test/suite/rpl/t/rpl_master_pos_wait.test

@@ -48,6 +48,7 @@ select master_pos_wait('master-bin.000001',1000000,1);
 
 --echo # Call with a valid connection name -- hangs before MDEV-7130 fix (expected -1)
 select master_pos_wait('master-bin.000001',1000000,1,"my_slave");
+select master_pos_wait('master-bin.000001',1000000,1,"MY_SLAVE");
 
 STOP SLAVE 'my_slave';
 RESET SLAVE 'my_slave' ALL;

sql/rpl_mi.cc

@@ -1369,27 +1369,21 @@ Master_info_index::get_master_info(const LEX_CSTRING *connection_name,
                                    Sql_condition::enum_warning_level warning)
 {
   Master_info *mi;
-  char buff[MAX_CONNECTION_NAME+1], *res;
-  size_t buff_length;
   DBUG_ENTER("get_master_info");
   DBUG_PRINT("enter",
              ("connection_name: '%.*s'", (int) connection_name->length,
               connection_name->str));
 
-  /* Make name lower case for comparison */
-  res= strmake(buff, connection_name->str, connection_name->length);
-  my_casedn_str(system_charset_info, buff); 
-  buff_length= (size_t) (res-buff);
-
+  if (!connection_name->str)
+    connection_name= &empty_clex_str;
   mi= (Master_info*) my_hash_search(&master_info_hash,
-                                    (uchar*) buff, buff_length);
+                                    (uchar*) connection_name->str,
+                                    connection_name->length);
   if (!mi && warning != Sql_condition::WARN_LEVEL_NOTE)
   {
     my_error(WARN_NO_MASTER_INFO,
-             MYF(warning == Sql_condition::WARN_LEVEL_WARN ? ME_WARNING :
-                 0),
-             (int) connection_name->length,
-             connection_name->str);
+             MYF(warning == Sql_condition::WARN_LEVEL_WARN ? ME_WARNING : 0),
+             (int) connection_name->length, connection_name->str);
   }
   DBUG_RETURN(mi);
 }