buf_LRU_block_free_non_file_page(): Deallocate block->page_zip.data
to avoid ut_a(!block->page_zip.data) in buf_chunk_free().

buf_chunk_free(): Add the assertion ut_a(!block->in_LRU_list).

buf_pool_resize(): When shrinking the buffer pool and there are
non-free blocks in the candidate chunk, free the clean blocks
and move the dirty blocks to the end of the LRU list and request a flush.
Proceed if the chunk becomes free, and retry otherwise.