LaTeX writer: avoid footnotes in list of figures.

Footnotes aren't allowed in the list of figures.  This
patch causes footnotes to be stripped from captions when
entered into the list of figures.

Footnotes still don't actually WORK in captions in latex/pdf,
but at least an error is no longer raised.

See #1506.

src/Text/Pandoc/Writers/LaTeX.hs

@@ -395,12 +395,17 @@ blockToLaTeX (Plain lst) =
 blockToLaTeX (Para [Image txt (src,'f':'i':'g':':':tit)]) = do
   inNote <- gets stInNote
   capt <- inlineListToLaTeX txt
+  -- We can't have footnotes in the list of figures, so remove them:
+  captForLof <- if null (query queryNote txt)
+                   then return empty
+                   else brackets <$> inlineListToLaTeX (walk deNote txt)
   img <- inlineToLaTeX (Image txt (src,tit))
   return $ if inNote
               -- can't have figures in notes
               then "\\begin{center}" $$ img $+$ capt $$ "\\end{center}"
               else "\\begin{figure}[htbp]" $$ "\\centering" $$ img $$
-                      ("\\caption" <> braces capt) $$ "\\end{figure}"
+                    ("\\caption" <> captForLof <> braces capt) $$
+                    "\\end{figure}"
 -- . . . indicates pause in beamer slides
 blockToLaTeX (Para [Str ".",Space,Str ".",Space,Str "."]) = do
   beamer <- writerBeamer `fmap` gets stOptions
@@ -1202,3 +1207,11 @@ commonFromBcp47 x = fromIso $ head x
     fromIso "ur"  = "urdu"
     fromIso "vi"  = "vietnamese"
     fromIso _     = ""
+
+queryNote :: Inline -> [Inline]
+queryNote (Note xs) = [Note xs]
+queryNote _ = []
+
+deNote :: Inline -> Inline
+deNote (Note _) = RawInline (Format "latex") ""
+deNote x = x