ipynb writer: don't create attachments for images with absolute URIs.

...including data: URIs.

Closes #5303.

src/Text/Pandoc/Writers/Ipynb.hs

@@ -49,7 +49,7 @@ import Data.Text (Text)
 import qualified Data.Text as T
 import Data.Aeson as Aeson
 import qualified Text.Pandoc.UTF8 as UTF8
-import Text.Pandoc.Shared (safeRead)
+import Text.Pandoc.Shared (safeRead, isURI)
 import Text.Pandoc.Writers.Shared (metaToJSON')
 import Text.Pandoc.Writers.Markdown (writeMarkdown)
 import qualified Data.Text.Encoding as TE
@@ -98,7 +98,8 @@ pandocToNotebook opts (Pandoc meta blocks) = do
 addAttachment :: PandocMonad m
               => Inline
               -> StateT (M.Map Text MimeBundle) m Inline
-addAttachment (Image attr lab (src,tit)) = do
+addAttachment (Image attr lab (src,tit))
+  | not (isURI src) = do
   (img, mbmt) <- fetchItem src
   let mt = maybe "application/octet-stream" (T.pack) mbmt
   modify $ M.insert (T.pack src)