LaTeX writer: add \protect to \hyperlink.

Thanks to Hadrien Mary for the problem and solution.

Closes #2490.

src/Text/Pandoc/Writers/LaTeX.hs

@@ -881,7 +881,7 @@ inlineToLaTeX Space = return space
 inlineToLaTeX (Link txt ('#':ident, _)) = do
   contents <- inlineListToLaTeX txt
   lab <- toLabel ident
-  return $ text "\\hyperlink" <> braces (text lab) <> braces contents
+  return $ text "\\protect\\hyperlink" <> braces (text lab) <> braces contents
 inlineToLaTeX (Link txt (src, _)) =
   case txt of
         [Str x] | escapeURI x == src ->  -- autolink

tests/Tests/Writers/LaTeX.hs

@@ -42,7 +42,7 @@ tests = [ testGroup "code blocks"
         , testGroup "definition lists"
           [ "with internal link" =: definitionList [(link "#go" "" (str "testing"),
              [plain (text "hi there")])] =?>
-            "\\begin{description}\n\\tightlist\n\\item[\\hyperlink{go}{testing}]\nhi there\n\\end{description}"
+            "\\begin{description}\n\\tightlist\n\\item[\\protect\\hyperlink{go}{testing}]\nhi there\n\\end{description}"
           ]
         , testGroup "math"
           [ "escape |" =: para (math "\\sigma|_{\\{x\\}}") =?>