Fix a few compiler warnings.  Fix crash with encrypted undo file.
diff --git a/src/blowfish.c b/src/blowfish.c
index 1ab8eca..d47f463 100644
--- a/src/blowfish.c
+++ b/src/blowfish.c
@@ -413,6 +413,11 @@
 
     key = sha256_key(password);
     keylen = (int)STRLEN(key);
+    if (keylen == 0)
+    {
+	EMSG(_("E831: bf_key_init() called with empty password"));
+	return;
+    }
     for (i = 0; i < 256; ++i)
     {
 	sbx[0][i] = sbi[0][i];