patch 8.2.3245: the crypt key may appear in a swap partition

Problem:    The crypt key may appear in a swap partition.
Solution:   When using xchaha20 use sodium_mlock(). (Christian Brabandt,
            closes #8657)
diff --git a/src/vim.h b/src/vim.h
index e45a1de..30cf284 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -486,6 +486,10 @@
 # endif
 #endif
 
+#ifdef HAVE_SODIUM
+# include <sodium.h>
+#endif
+
 // ================ end of the header file puzzle ===============
 
 /*