Fixed over-eager raw HTML inline parsing.

Tightened up the inline HTML parser so it disallows
TagWarnings.

This only affects the markdown reader when the `markdown_in_html_blocks`
option is disabled.

Closes #2469.

src/Text/Pandoc/Readers/HTML.hs

@@ -948,6 +948,7 @@ htmlTag f = try $ do
                        parseOptions{ optTagWarning = True } inp
   guard $ f next
   case next of
+       TagWarning _ -> fail "encountered TagWarning"
        TagComment s
          | "<!--" `isPrefixOf` inp -> do
           count (length s + 4) anyChar

tests/Tests/Readers/Markdown.hs

@@ -181,6 +181,9 @@ tests = [ testGroup "inline code"
           , "technically invalid comment" =:
             "<!-- pandoc --help -->" =?>
             rawBlock "html" "<!-- pandoc --help -->"
+          , test markdownGH "issue 2469" $
+            "<\n\na>" =?>
+            para (text "<") <> para (text "a>")
           ]
         , "unbalanced brackets" =:
             "[[[[[[[[[[[[[[[hi" =?> para (text "[[[[[[[[[[[[[[[hi")