LaTeX writer: separate successive quote chars with thin space

Successive quote characters are separated with a thin space to improve
readability and to prevent unwanted ligatures. Detection of these quotes
sometimes had failed if the second quote was nested in a span element.

Closes: #6958

src/Text/Pandoc/Writers/LaTeX.hs

@@ -894,8 +894,9 @@ inlineToLaTeX (Quoted qt lst) = do
                       then char '`' <> inner <> char '\''
                       else char '\x2018' <> inner <> char '\x2019'
     where
-      isQuoted (Quoted _ _) = True
-      isQuoted _            = False
+      isQuoted (Span _ (x:_)) = isQuoted x
+      isQuoted (Quoted _ _)   = True
+      isQuoted _              = False
 inlineToLaTeX (Str str) = do
   setEmptyLine False
   liftM literal $ stringToLaTeX TextString str

test/command/6958.md

@@ -0,0 +1,10 @@
+Add thin space between single and double quotes.
+```
+% pandoc -t latex+smart
+---
+lang: en-GB
+---
+'["On the Outside"]{}: Constructing Cycling Citizenship.'
+^D
+`\,{``On the Outside''}: Constructing Cycling Citizenship.'
+```