MDEV-14868 MariaDB server crashes after using ROLLBACK TO when encrypt_tmp_files=ON

Fix reinit_io_cache(WRITE_CACHE) with non-zero seek_offset.
Run encryption.tempfiles with and without binlog checksums.

mysql-test/suite/encryption/t/tempfiles.combinations

@@ -0,0 +1,5 @@
+[none]
+binlog-checksum=NONE
+
+[crc32]
+binlog-checksum=CRC32

mysys/mf_iocache.c

@@ -440,7 +440,7 @@ my_bool reinit_io_cache(IO_CACHE *info, enum cache_type type,
           info->read_end= info->buffer;
           _my_b_encr_read(info, 0, 0); /* prefill the buffer */
           info->write_pos= info->read_pos;
-          info->pos_in_file+= info->buffer_length;
+          info->seek_not_done=1;
         }
       }
       else

sql/mf_iocache_encr.cc

@@ -145,9 +145,10 @@ static int my_b_encr_write(IO_CACHE *info, const uchar *Buffer, size_t Count)
 
   if (info->seek_not_done)
   {
-    DBUG_ASSERT(info->pos_in_file == 0);
+    DBUG_ASSERT(info->pos_in_file % info->buffer_length == 0);
+    size_t wpos= info->pos_in_file / info->buffer_length * crypt_data->block_length;
 
-    if ((mysql_file_seek(info->file, 0, MY_SEEK_SET, MYF(0)) == MY_FILEPOS_ERROR))
+    if ((mysql_file_seek(info->file, wpos, MY_SEEK_SET, MYF(0)) == MY_FILEPOS_ERROR))
     {
       info->error= -1;
       DBUG_RETURN(1);