Vimwiki reader: test empty preformatted text

test/vimwiki-reader.native

@@ -49,6 +49,8 @@ Pandoc (Meta {unMeta = fromList [("date",MetaInlines [Str "2017-05-01"]),("title
 ,CodeBlock ("",[],[]) "  Tyger! Tyger! burning bright\n   In the forests of the night,\n    What immortal hand or eye\n     Could frame thy fearful symmetry?\n  In what distant deeps or skies\n   Burnt the fire of thine eyes?\n    On what wings dare he aspire?\n     What the hand dare sieze the fire?"
 ,Header 3 ("preformatted text with attributes",[],[]) [Str "preformatted",Space,Str "text",Space,Str "with",Space,Str "attributes"]
 ,CodeBlock ("",[],[("class","python"),("style","color:blue")]) " for i in range(1, 5):\n     print(i)"
+,Header 3 ("empty preformatted text",[],[]) [Str "empty",Space,Str "preformatted",Space,Str "text"]
+,CodeBlock ("",[],[]) ""
 ,Header 2 ("block quotes",[],[]) [Str "block",Space,Str "quotes"]
 ,BlockQuote
  [Plain [Str "(indentation",Space,Str "4",Space,Str "spaces)",Space,Str "This",Space,Str "would",Space,Str "be",Space,Str "a",Space,Str "blockquote",Space,Str "in",Space,Str "Vimwiki.",Space,Str "It",Space,Str "is",Space,Str "not",Space,Span ("highlighted",[],[]) [],Strong [Str "highlighted"],Space,Str "in",Space,Str "Vim",Space,Str "but",SoftBreak,Str "(indentation",Space,Str "1",Space,Str "space",Space,Str "followed",Space,Str "by",Space,Str "1",Space,Str "tab",Space,Str "of",Space,Str "width",Space,Str "4)",Space,Str "could",Space,Str "be",Space,Str "styled",Space,Str "by",Space,Str "CSS",Space,Str "in",Space,Str "HTML.",Space,Str "Blockquotes",Space,Str "are",Space,Str "usually",Space,Str "used",Space,Str "to",Space,Str "quote",Space,Str "a",SoftBreak,Str "(indentation",Space,Str "1",Space,Str "tab",Space,Str "of",Space,Str "width",Space,Str "4)",Space,Str "long",Space,Str "piece",Space,Str "of",Space,Str "text",Space,Str "from",Space,Str "another",Space,Str "source.",Space,Strikeout [Str "blah",Space,Str "blah"],Space,Span ("-blockquote",[],[]) [Str ""],Span ("blockquote",["tag"],[]) [Str "blockquote"]]]

test/vimwiki-reader.wiki

@@ -116,7 +116,12 @@ Just two backticks: ``
  for i in range(1, 5):
      print(i)
  }}}
- 
+
+=== empty preformatted text ===
+
+{{{
+}}}
+
 == block quotes ==
 
     (indentation 4 spaces) This would be a blockquote in Vimwiki. It is not *highlighted* in Vim but