Markdown writer: fix bug with block quotes in lists.

Closes #9908.

src/Text/Pandoc/Writers/Markdown.hs

@@ -592,7 +592,7 @@ blockToMarkdown' opts (BlockQuote blocks) = do
         | variant == PlainText = "  "
         | otherwise            = "> "
   contents <- blockListToMarkdown opts blocks
-  return $ prefixed leader contents <> blankline
+  return $ text leader <> prefixed leader contents <> blankline
 blockToMarkdown' opts t@(Table (ident,_,_) blkCapt specs thead tbody tfoot) = do
   let (caption, aligns, widths, headers, rows) = toLegacyTable blkCapt specs thead tbody tfoot
   let numcols = maximum (length aligns :| length widths :

test/command/9908.md

@@ -0,0 +1,10 @@
+```
+% pandoc -f native -t markdown
+[ BulletList
+    [ [ BlockQuote [ Para [ Str "a" ] , Para [ Str "b" ] ] ] ]
+]
+^D
+-   > a
+    >
+    > b
+```