branches/zip: buf_page_init_for_read(): Decrement, do not reset

block->page.buf_fix_count.  This mistake was made in r1255.
When access to the block is requested by some other thread,
buf_fix_count can be incremented during the execution of
buf_zip_decompress().

buf/buf0buf.c

@@ -2320,7 +2320,7 @@ buf_page_init_for_read(
 			/* Unfix and unlatch the block. */
 			mutex_enter(&buf_pool->mutex);
 			mutex_enter(&block->mutex);
-			block->page.buf_fix_count = 0;
+			block->page.buf_fix_count--;
 			buf_block_set_io_fix(block, BUF_IO_NONE);
 			mutex_exit(&buf_pool->mutex);
 			mutex_exit(&block->mutex);