LaTeX writer: Use \endhead after \toprule in headerless tables.

Closes #4207.

src/Text/Pandoc/Writers/LaTeX.hs

@@ -699,10 +699,9 @@ blockToLaTeX (Table caption aligns widths heads rows) = do
                   then return empty
                   else ($$ text "\\endfirsthead") <$> toHeaders heads
   head' <- if all null heads
-              then return empty
+              then return "\\toprule"
               -- avoid duplicate notes in head and firsthead:
-              else ($$ text "\\endhead") <$>
-                   toHeaders (if isEmpty firsthead
+              else toHeaders (if isEmpty firsthead
                                  then heads
                                  else walk removeNote heads)
   let capt = if isEmpty captionText
@@ -717,8 +716,8 @@ blockToLaTeX (Table caption aligns widths heads rows) = do
               -- the @{} removes extra space at beginning and end
          $$ capt
          $$ firsthead
-         $$ (if all null heads then "\\toprule" else empty)
          $$ head'
+         $$ "\\endhead"
          $$ vcat rows'
          $$ "\\bottomrule"
          $$ "\\end{longtable}"

test/tables.latex

@@ -136,6 +136,7 @@ Table without column headers:
 
 \begin{longtable}[]{@{}rlcr@{}}
 \toprule
+\endhead
 12 & 12 & 12 & 12\tabularnewline
 123 & 123 & 123 & 123\tabularnewline
 1 & 1 & 1 & 1\tabularnewline
@@ -146,6 +147,7 @@ Multiline table without column headers:
 
 \begin{longtable}[]{@{}clrl@{}}
 \toprule
+\endhead
 \begin{minipage}[t]{0.13\columnwidth}\centering
 First\strut
 \end{minipage} & \begin{minipage}[t]{0.12\columnwidth}\raggedright