Markdown reader: fix parsing of inline math ($...$) (#11348)

Do not allow blank lines before closing `$` delimiter.
This brings the parser in line with the documentation.

Closes #11311.

Author: benniekiss

src/Text/Pandoc/Parsing/Math.hs

@@ -42,7 +42,7 @@ mathInlineWith op cl = try $ do
                            (try (string "text" >>
                                  (("\\text" <>) <$> inBalancedBraces 0 ""))
                             <|>  (\c -> T.pack ['\\',c]) <$> anyChar))
-                   <|> ("\n" <$ blankline <* notFollowedBy' blankline)
+                   <|> ("\n" <$ blankline <* notFollowedBy' blankline <* notFollowedBy (char '$'))
                    <|> (T.pack <$> many1 spaceChar <* notFollowedBy (char '$'))
                     ) (try $ textStr cl)
   notFollowedBy digit  -- to prevent capture of $5

test/command/11348.md

@@ -0,0 +1,61 @@
+```
+% pandoc -f markdown -t native
+$ invalid opening inline math$
+
+$
+invalid opening inline math$
+
+$invalid closing inline math $
+
+$invalid closing inline math
+$
+
+$valid inline math$
+^D
+[ Para
+    [ Str "$"
+    , Space
+    , Str "invalid"
+    , Space
+    , Str "opening"
+    , Space
+    , Str "inline"
+    , Space
+    , Str "math$"
+    ]
+, Para
+    [ Str "$"
+    , SoftBreak
+    , Str "invalid"
+    , Space
+    , Str "opening"
+    , Space
+    , Str "inline"
+    , Space
+    , Str "math$"
+    ]
+, Para
+    [ Str "$invalid"
+    , Space
+    , Str "closing"
+    , Space
+    , Str "inline"
+    , Space
+    , Str "math"
+    , Space
+    , Str "$"
+    ]
+, Para
+    [ Str "$invalid"
+    , Space
+    , Str "closing"
+    , Space
+    , Str "inline"
+    , Space
+    , Str "math"
+    , SoftBreak
+    , Str "$"
+    ]
+, Para [ Math InlineMath "valid inline math" ]
+]
+```