Enlarged group item key_length by a varstring length field.

Group item fields are implemented as varstrings nowadays.
Made init_connect.test robust against existing t1.

mysql-test/r/init_connect.result

@@ -12,7 +12,7 @@ set GLOBAL init_connect=DEFAULT;
 select @a;
 @a
 NULL
-set global init_connect="create table t1(a char(10));\
+set global init_connect="drop table if exists t1; create table t1(a char(10));\
 insert into t1 values ('\0');insert into t1 values('abc')";
 select hex(a) from t1;
 hex(a)

mysql-test/t/init_connect.test

@@ -19,7 +19,7 @@ connect (con3,localhost,user_1,,);
 connection con3;
 select @a;
 connection con0;
-set global init_connect="create table t1(a char(10));\
+set global init_connect="drop table if exists t1; create table t1(a char(10));\
 insert into t1 values ('\0');insert into t1 values('abc')";
 connect (con4,localhost,user_1,,);
 connection con4;

sql/sql_select.cc

@@ -11654,8 +11654,21 @@ calc_group_buffer(JOIN *join,ORDER *group)
       key_length+=sizeof(double);
     else if ((*group->item)->result_type() == INT_RESULT)
       key_length+=sizeof(longlong);
+    else if ((*group->item)->result_type() == STRING_RESULT)
+    {
+      /*
+        Group strings are taken as varstrings and require an length field.
+        A field is not yet created by create_tmp_field()
+        and the sizes should match up.
+      */
+      key_length+= (*group->item)->max_length + HA_KEY_BLOB_LENGTH;
+    }
     else
-      key_length+=(*group->item)->max_length;
+    {
+      /* This case should never be choosen */
+      DBUG_ASSERT(0);
+      current_thd->fatal_error();
+    }
     parts++;
     if ((*group->item)->maybe_null)
       null_parts++;