MDEV-24668 debug assert on SET PASSWORD when binlog fails

don't use `result` both for an error status and to remember
if the mutex was locked

mysql-test/suite/binlog/r/binlog_write_error.result

@@ -100,6 +100,12 @@ ERROR HY000: Error writing file 'master-bin' ((errno: #)
 set @@global.debug_dbug = @saved_dbug;
 set @saved_dbug = @@global.debug_dbug;
 SET GLOBAL debug_dbug='d,injecting_fault_writing';
+SET PASSWORD FOR user1=PASSWORD('foobar');
+SET PASSWORD FOR user1=PASSWORD('foobar');
+ERROR HY000: Error writing file 'master-bin' ((errno: #)
+set @@global.debug_dbug = @saved_dbug;
+set @saved_dbug = @@global.debug_dbug;
+SET GLOBAL debug_dbug='d,injecting_fault_writing';
 DROP USER user1;
 DROP USER user1;
 ERROR HY000: Error writing file 'master-bin' ((errno: #)

mysql-test/suite/binlog/t/binlog_write_error.test

@@ -75,5 +75,8 @@ source include/binlog_inject_error.inc;
 let $query= REVOKE ALL PRIVILEGES, GRANT OPTION FROM user1;
 source include/binlog_inject_error.inc;
 
+let $query= SET PASSWORD FOR user1=PASSWORD('foobar');
+source include/binlog_inject_error.inc;
+
 let $query= DROP USER user1;
 source include/binlog_inject_error.inc;

mysql-test/suite/binlog_encryption/binlog_write_error.result

@@ -100,6 +100,12 @@ ERROR HY000: Error writing file 'master-bin' ((errno: #)
 set @@global.debug_dbug = @saved_dbug;
 set @saved_dbug = @@global.debug_dbug;
 SET GLOBAL debug_dbug='d,injecting_fault_writing';
+SET PASSWORD FOR user1=PASSWORD('foobar');
+SET PASSWORD FOR user1=PASSWORD('foobar');
+ERROR HY000: Error writing file 'master-bin' ((errno: #)
+set @@global.debug_dbug = @saved_dbug;
+set @saved_dbug = @@global.debug_dbug;
+SET GLOBAL debug_dbug='d,injecting_fault_writing';
 DROP USER user1;
 DROP USER user1;
 ERROR HY000: Error writing file 'master-bin' ((errno: #)

sql/sql_acl.cc

@@ -3794,7 +3794,7 @@ bool change_password(THD *thd, LEX_USER *user)
   char buff[512];
   ulong query_length= 0;
   enum_binlog_format save_binlog_format;
-  int result=0;
+  bool result, acl_cache_is_locked= false;
   ACL_USER *acl_user;
   ACL_USER::AUTH auth;
   const char *password_plugin= 0;
@@ -3819,7 +3819,7 @@ bool change_password(THD *thd, LEX_USER *user)
   if ((result= tables.open_and_lock(thd, Table_user, TL_WRITE)))
     DBUG_RETURN(result != 1);
 
-  result= 1;
+  acl_cache_is_locked= 1;
   mysql_mutex_lock(&acl_cache->lock);
 
   if (!(acl_user= find_user_exact(user->host.str, user->user.str)))
@@ -3872,7 +3872,7 @@ bool change_password(THD *thd, LEX_USER *user)
 
   acl_cache->clear(1);                          // Clear locked hostname cache
   mysql_mutex_unlock(&acl_cache->lock);
-  result= 0;
+  result= acl_cache_is_locked= 0;
   if (mysql_bin_log.is_open())
   {
     query_length= sprintf(buff, "SET PASSWORD FOR '%-.120s'@'%-.120s'='%-.120s'",
@@ -3883,7 +3883,7 @@ bool change_password(THD *thd, LEX_USER *user)
                               FALSE, FALSE, FALSE, 0) > 0;
   }
 end:
-  if (result)
+  if (acl_cache_is_locked)
     mysql_mutex_unlock(&acl_cache->lock);
   close_mysql_tables(thd);