fix ASAN: nullable fields require more space

mysql-test/suite/period/r/overlaps.result

@@ -104,7 +104,7 @@ show create table t;
 Table	Create Table
 t	CREATE TABLE `t` (
   `id` int(11) NOT NULL,
-  `u` int(11) DEFAULT NULL,
+  `u` int(11) NOT NULL,
   `s` date NOT NULL,
   `e` date NOT NULL,
   PERIOD FOR `p` (`s`, `e`),

sql/sql_table.cc

@@ -3959,6 +3959,28 @@ mysql_prepare_create_table(THD *thd, HA_CREATE_INFO *create_info,
         DBUG_RETURN(TRUE);
       }
 
+      switch (key->type) {
+        case Key::UNIQUE:
+          if (!key->period)
+            break;
+          /* Fall through:
+             WITHOUT OVERLAPS forces fields to be NOT NULL
+           */
+        case Key::PRIMARY:
+          /* Implicitly set primary key fields to NOT NULL for ISO conf. */
+          if (!(sql_field->flags & NOT_NULL_FLAG))
+          {
+            /* Implicitly set primary key fields to NOT NULL for ISO conf. */
+            sql_field->flags|= NOT_NULL_FLAG;
+            sql_field->pack_flag&= ~FIELDFLAG_MAYBE_NULL;
+            null_fields--;
+          }
+          break;
+        default:
+          // Fall through
+          break;
+      }
+
       cols2.rewind();
       switch(key->type) {
 
@@ -3996,13 +4018,6 @@ mysql_prepare_create_table(THD *thd, HA_CREATE_INFO *create_info,
 	                                                          *sql_field,
 	                                                          file))
           DBUG_RETURN(TRUE);
-        if (!(sql_field->flags & NOT_NULL_FLAG))
-        {
-          /* Implicitly set primary key fields to NOT NULL for ISO conf. */
-          sql_field->flags|= NOT_NULL_FLAG;
-          sql_field->pack_flag&= ~FIELDFLAG_MAYBE_NULL;
-          null_fields--;
-        }
         break;
 
       case Key::MULTIPLE: