patch 9.0.1481: decrypting with libsodium may fail if the library changes

Problem:    Decrypting with libsodium may fail if the library changes.
Solution:   Add parameters used to the encrypted file header. (Christian
            Brabandt, closes #12279)
diff --git a/src/buffer.c b/src/buffer.c
index 6d4c435..98cca6c 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -2362,8 +2362,8 @@
 #endif
 #ifdef FEAT_CRYPT
 # ifdef FEAT_SODIUM
-    if ((buf->b_p_key != NULL) && (*buf->b_p_key != NUL) &&
-				(crypt_get_method_nr(buf) == CRYPT_M_SOD))
+    if (buf->b_p_key != NULL && *buf->b_p_key != NUL
+			   && crypt_method_is_sodium(crypt_get_method_nr(buf)))
 	crypt_sodium_munlock(buf->b_p_key, STRLEN(buf->b_p_key));
 # endif
     clear_string_option(&buf->b_p_key);