allocating compressed page frames or their control blocks.  Also note
that if buf_buddy_alloc() is used for allocating a control block,
it must be initialized before releasing buf_pool->mutex.

buf_page_init_for_read(): When the page hash check fails after
buf_buddy_alloc(), free the uninitialized control block before freeing
the compressed page frame.  This fixes a potential error in
buf_buddy_relocate_block().