Use open_in_bin not open_in for merlinpp (#1725)

from jonahbeckford/fix-file-open-win32

Author: voodoos

CHANGES.md

@@ -9,6 +9,7 @@ merlin NEXT_VERSION
     - Add a query_num field to the `ocamlmerlin` responses to detect server crashes (#1716)
   + editor modes
     - vim: load merlin under the ocamlinterface and ocamllex filetypes (#1340)
+    - Fix merlinpp not using binary file open (#1725, fixes #1724)
 
 merlin 4.13
 ===========

src/ocaml/driver/pparse.ml

@@ -177,7 +177,7 @@ let apply_pp ~workdir ~filename ~source ~pp =
   end else if not (Sys.file_exists fn_out) then
     Error (WrongMagic comm)
   else
-    let ic = open_in fn_out in
+    let ic = open_in_bin fn_out in
     let result = Misc.string_of_file ic in
     close_in ic;
     Ok result