T.P.Class.IO.openURL improvements for data uris.

- Only treat as base64 if ';base64' is present.
- Otherwise treat as UTF-8 (not 100% reliable but should cover most
  other cases).
- Strip off ';base64' (or ';charset=...' or whatever) from mime type.

This last change addresses #9195 (problems with data URIs in
conversion to docx).

src/Text/Pandoc/Class/IO.hs

@@ -124,9 +124,13 @@ openURL :: (PandocMonad m, MonadIO m) => Text -> m (B.ByteString, Maybe MimeType
 openURL u
  | Just (URI{ uriScheme = "data:",
               uriPath = upath }) <- parseURI (T.unpack u) = do
-     let (mime, rest) = break (== ',') $ unEscapeString upath
+     let (mimespec, rest) = break (== ',') $ unEscapeString upath
      let contents = UTF8.fromString $ drop 1 rest
-     return (decodeBase64Lenient contents, Just (T.pack mime))
+     case break (== ';') (filter (/= ' ') mimespec) of
+       (mime, ";base64") ->
+         return (decodeBase64Lenient contents, Just (T.pack mime))
+       (mime, _) ->
+         return (contents, Just (T.pack mime))
  | otherwise = do
      let toReqHeader (n, v) = (CI.mk (UTF8.fromText n), UTF8.fromText v)
      customHeaders <- map toReqHeader <$> getsCommonState stRequestHeaders