patch 8.2.3032: build problems with MSVC, other crypt issues with libsodium

Problem:    Build problems with MSVC, other crypt issues with libsodium.
Solution:   Adjust MSVC makefile. Disable swap file only when 'key' is set.
            Adjust error message used when key is wrong.  Fix Coverity issues.
            (Christian Brabandt, closes #8420, closes #8411)
diff --git a/src/errors.h b/src/errors.h
index 9663ecd..8a2461b 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -443,6 +443,6 @@
 EXTERN char e_libsodium_cannot_decrypt_buffer[]
 	INIT(= N_("E1199: Cannot decrypt buffer, not enough space"));
 EXTERN char e_libsodium_decryption_failed[]
-	INIT(= N_("E1200: Decryption failed: corrupted chunk!"));
+	INIT(= N_("E1200: Decryption failed!"));
 EXTERN char e_libsodium_decryption_failed_premature[]
 	INIT(= N_("E1201: Decryption failed: pre-mature end of file!"));