MDEV-13798 - fix incorrect alignment of the buffer in incremental backup

This incorrect alignment can later lead to memcpy over buffer boundaries,
and to a crash.

extra/mariabackup/write_filt.cc

@@ -79,7 +79,7 @@ wf_incremental_init(xb_write_filt_ctxt_t *ctxt, char *dst_name,
 	cp->delta_buf_base = static_cast<byte *>(ut_malloc(buf_size));
 	memset(cp->delta_buf_base, 0, buf_size);
 	cp->delta_buf = static_cast<byte *>
-		(ut_align(cp->delta_buf_base, UNIV_PAGE_SIZE_MAX));
+		(ut_align(cp->delta_buf_base, cursor->page_size));
 
 	/* write delta meta info */
 	snprintf(meta_name, sizeof(meta_name), "%s%s", dst_name,