fix encoding of metadata containing newlines

This fixes a reversion in the ByteString conversion. The old code used
isSpace to decide when the metadata value needs to be base64 encoded,
and that incorrectly changed to only checking if it contained ' '.

Note that only '\n' and '\r' were added and not other sorts of
whitespace that isSpace matches, like '\t' and '\v'. Only the former
would cause problems.

Types/MetaData.hs

@@ -136,7 +136,7 @@ instance MetaSerializable MetaField where
 instance MetaSerializable MetaValue where
 	serialize (MetaValue isset v) =
 		serialize isset <>
-		if B8.any (== ' ') v || "!" `B8.isPrefixOf` v
+		if B8.any (`elem` [' ', '\r', '\n']) v || "!" `B8.isPrefixOf` v
 			then "!" <> toB64' v
 			else v
 	deserialize b = do