patch 8.2.3022: available encryption methods are not strong enough

Problem:    Available encryption methods are not strong enough.
Solution:   Add initial support for xchaha20. (Christian Brabandt,
            closes #8394)
diff --git a/src/option.c b/src/option.c
index 535213c..07bb71e 100644
--- a/src/option.c
+++ b/src/option.c
@@ -2713,6 +2713,10 @@
 				|| (opt_flags & OPT_GLOBAL) || opt_flags == 0)
 			&& !curbufIsChanged() && curbuf->b_ml.ml_mfp != NULL)
 		{
+#ifdef FEAT_CRYPT
+		    if (crypt_get_method_nr(curbuf) == CRYPT_M_SOD)
+			continue;
+#endif
 		    u_compute_hash(hash);
 		    u_read_undo(NULL, hash, curbuf->b_fname);
 		}