updated for version 7.4.509

Problem:    Users are not aware their encryption is weak.
Solution:   Give a warning when prompting for the key.

src/fileio.c

@@ -2958,6 +2958,7 @@ check_for_cryptkey(cryptkey, ptr, sizep, filesizep, newfile, fname, did_ask)
 		 * Happens when retrying to detect encoding. */
 		smsg((char_u *)_(need_key_msg), fname);
 		msg_scroll = TRUE;
+		crypt_check_method(method);
 		cryptkey = crypt_get_key(newfile, FALSE);
 		*did_ask = TRUE;