Typst reader: fix an incomplete pattern match.

See #9807.

src/Text/Pandoc/Readers/Typst.hs

@@ -105,8 +105,10 @@ pInline = try $ do
           B.math . writeTeX <$> pMathMany (Seq.singleton res)
     Elt name@(Identifier tname) pos fields -> do
       labs <- sLabels <$> getState
-      labelTarget <- (do VLabel t <- getField "target" fields
-                         True <$ guard (t `elem` labs))
+      labelTarget <- (do result <- getField "target" fields
+                         case result of
+                           VLabel t | t `elem` labs -> pure True
+                           _ -> pure False)
                   <|> pure False
       if tname == "ref" && not labelTarget
          then do