Fix semantics (and documentation) for -newpage

cpdfdraw.ml

@@ -435,9 +435,14 @@ let draw ?(fast=false) ?(underneath=false) ~filename ~bates ~batespad range pdf
       if hd !chunks <> [] then pdf := draw_single ~fast ~underneath ~filename ~bates ~batespad fast !range !pdf (hd !chunks);
       chunks := tl !chunks;
       if !chunks <> [] then begin
+        (* If the range is just a single page, and there is a next page, move to it. Otherwise,
+           add a blank page at the end of the document. *)
         let endpage = Pdfpage.endpage !pdf in
-          pdf := Cpdfpad.padafter [endpage] !pdf;
-          range := [endpage + 1]
+          match !range with
+          | [x] when endpage > x -> range := [x + 1]
+          | _ ->
+              pdf := Cpdfpad.padafter [endpage] !pdf;
+              range := [endpage + 1]
       end
     done;
     !pdf

cpdfmanual.tex

@@ -4619,7 +4619,7 @@ NB: To use \texttt{-embed-std14}, put it before \texttt{-draw}.
    \noindent\verb!-newpage! Move to a fresh page
   \end{framed}}
 
-The drawing operation \texttt{-newpage} creates a fresh page of the same dimensions as the last page of the document, and sets the drawing range to just that page. For example:
+If the drawing range is a single page, and the next page already exists, the drawing operation \texttt{-newpage} operation moves to the next page. Otherwise, it creates a fresh page of the same dimensions as the last page of the document, and sets the drawing range to just that page. For example:
 
 \begin{framed}
  \noindent\small\verb?cpdf -create-pdf AND -draw -bt -text "Page 1" -et?\\