WL 2826: Error handling of ALTER TABLE for partitioning

More review fixes

sql/mysql_priv.h

@@ -1266,6 +1266,12 @@ typedef struct st_ddl_log_entry
   uint entry_pos;
   enum ddl_log_entry_code entry_type;
   enum ddl_log_action_code action_type;
+  /*
+    Most actions have only one phase. REPLACE does however have two
+    phases. The first phase removes the file with the new name if
+    there was one there before and the second phase renames the
+    old name to the new name.
+  */
   char phase;
 } DDL_LOG_ENTRY;
 

sql/sql_partition.cc

@@ -5634,7 +5634,8 @@ static void write_log_completed(ALTER_PARTITION_PARAM_TYPE *lpt,
       Failed to write, Bad...
       We have completed the operation but have log records to REMOVE
       stuff that shouldn't be removed. What clever things could one do
-      here?
+      here? An error output was written to the error output by the
+      above method so we don't do anything here.
     */
     ;
   }