branches/zip: The block can't be in io fix state WRITE and we check for

that in the fix but the earlier check fails because it tries to be too
strict and assumes that if the block is on the clean list then it can
only be in state io fix NONE.

buf/buf0buf.c

@@ -3494,7 +3494,7 @@ buf_get_latched_pages_number(void)
 	for (b = UT_LIST_GET_FIRST(buf_pool->zip_clean); b;
 	     b = UT_LIST_GET_NEXT(list, b)) {
 		ut_a(buf_page_get_state(b) == BUF_BLOCK_ZIP_PAGE);
-		ut_a(buf_page_get_io_fix(b) == BUF_IO_NONE);
+		ut_a(buf_page_get_io_fix(b) != BUF_IO_WRITE);
 
 		if (b->buf_fix_count != 0
 		    || buf_page_get_io_fix(b) != BUF_IO_NONE) {