LaTeX writer: ensure that -M csquotes works even in fragment mode.

Closes #6265.

src/Text/Pandoc/Writers/LaTeX.hs

@@ -155,7 +155,8 @@ pandocToLaTeX options (Pandoc meta blocks) = do
                                           _               -> "article"
   when (documentClass `elem` chaptersClasses) $
      modify $ \s -> s{ stHasChapters = True }
-  case T.toLower . render Nothing <$> getField "csquotes" metadata of
+  case lookupContext "csquotes" (writerVariables options) `mplus`
+       (stringify <$> lookupMeta "csquotes" meta) of
      Nothing      -> return ()
      Just "false" -> return ()
      Just _       -> modify $ \s -> s{stCsquotes = True}

test/command/6265.md

@@ -0,0 +1,6 @@
+```
+% pandoc -f markdown -t latex -M csquotes=true
+"test"
+^D
+\enquote{test}
+```