branches/zip: buf_page_init_for_read(): Increment the buf_fix_count

during the buf_zip_decompress() call.  Otherwise, the block may end
up being freed by another thread.  This bug was caught by the
page_zip_validate() check in buf_LRU_block_remove_hashed_page().

buf/buf0buf.c

@@ -2161,6 +2161,8 @@ buf_page_init_for_read(
 				}
 			}
 
+			ut_a(!block->page.buf_fix_count);
+			block->page.buf_fix_count++;;
 			rw_lock_x_lock(&block->lock);
 			mutex_exit(&block->mutex);
 			mutex_exit(&buf_pool->zip_mutex);
@@ -2175,6 +2177,9 @@ buf_page_init_for_read(
 			}
 
 			buf_zip_decompress(block, srv_use_checksums);
+			mutex_enter(&block->mutex);
+			block->page.buf_fix_count--;
+			mutex_exit(&block->mutex);
 			rw_lock_x_unlock(&block->lock);
 
 			return(NULL);