video/readers/jpeg: Do not reallocate a given huff table

Fix a memory leak where an invalid file could cause us to reallocate
memory for a huffman table we had already allocated memory for.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/video/readers/jpeg.c

@@ -251,6 +251,9 @@ grub_jpeg_decode_huff_table (struct grub_jpeg_data *data)
 	n += count[i];
 
       id += ac * 2;
+      if (data->huff_value[id] != NULL)
+	return grub_error (GRUB_ERR_BAD_FILE_TYPE,
+			   "jpeg: attempt to reallocate huffman table");
       data->huff_value[id] = grub_malloc (n);
       if (grub_errno)
 	return grub_errno;