Bug#48276: can't add column if subpartition exists

Bug when setting up default partitioning,
used an uninitialized variabe.

mysql-test/r/partition.result

 drop table if exists t1, t2;
+CREATE TABLE t1 (a INT, b INT)
+PARTITION BY LIST (a)
+SUBPARTITION BY HASH (b)
+(PARTITION p1 VALUES IN (1));
+ALTER TABLE t1 ADD COLUMN c INT;
+DROP TABLE t1;
 CREATE TABLE t1 (
 a int NOT NULL,
 b int NOT NULL);

mysql-test/t/partition.test

@@ -14,6 +14,15 @@
 drop table if exists t1, t2;
 --enable_warnings
 
+#
+# Bug#48276: can't add column if subpartition exists
+CREATE TABLE t1 (a INT, b INT)
+PARTITION BY LIST (a)
+SUBPARTITION BY HASH (b)
+(PARTITION p1 VALUES IN (1));
+ALTER TABLE t1 ADD COLUMN c INT;
+DROP TABLE t1;
+
 #
 # Bug#46639: 1030 (HY000): Got error 124 from storage engine on
 # INSERT ... SELECT ...

sql/sql_partition.cc

@@ -196,26 +196,27 @@ bool partition_default_handling(TABLE *table, partition_info *part_info,
 {
   DBUG_ENTER("partition_default_handling");
 
-  if (part_info->use_default_no_partitions)
+  if (!is_create_table_ind)
   {
-    if (!is_create_table_ind &&
-        table->file->get_no_parts(normalized_path, &part_info->no_parts))
+    if (part_info->use_default_no_partitions)
     {
-      DBUG_RETURN(TRUE);
+      if (table->file->get_no_parts(normalized_path, &part_info->no_parts))
+      {
+        DBUG_RETURN(TRUE);
+      }
     }
-  }
-  else if (part_info->is_sub_partitioned() &&
-           part_info->use_default_no_subpartitions)
-  {
-    uint no_parts;
-    if (!is_create_table_ind &&
-        (table->file->get_no_parts(normalized_path, &no_parts)))
+    else if (part_info->is_sub_partitioned() &&
+             part_info->use_default_no_subpartitions)
     {
-      DBUG_RETURN(TRUE);
+      uint no_parts;
+      if (table->file->get_no_parts(normalized_path, &no_parts))
+      {
+        DBUG_RETURN(TRUE);
+      }
+      DBUG_ASSERT(part_info->no_parts > 0);
+      DBUG_ASSERT((no_parts % part_info->no_parts) == 0);
+      part_info->no_subparts= no_parts / part_info->no_parts;
     }
-    DBUG_ASSERT(part_info->no_parts > 0);
-    part_info->no_subparts= no_parts / part_info->no_parts;
-    DBUG_ASSERT((no_parts % part_info->no_parts) == 0);
   }
   part_info->set_up_defaults_for_partitioning(table->file,
                                               (ulonglong)0, (uint)0);