patch 8.2.4354: dynamic loading of libsodium not handled properly

Problem:    Dynamic loading of libsodium not handled properly.
Solution:   Fix has() and :version. Show an error message when loading fails.
            Fix memory leaks. (Ken Takata, closes #9754)
diff --git a/src/proto/crypt.pro b/src/proto/crypt.pro
index 682fe45..d6c7b7f 100644
--- a/src/proto/crypt.pro
+++ b/src/proto/crypt.pro
@@ -1,4 +1,5 @@
 /* crypt.c */
+int sodium_enabled(int verbose);
 int crypt_method_nr_from_name(char_u *name);
 int crypt_method_nr_from_magic(char *ptr, int len);
 int crypt_works_inplace(cryptstate_T *state);