fix wrong dialog kind used when saving doc as html

CHANGELOG.md

@@ -9,6 +9,7 @@ See [LDC announcement](https://forum.dlang.org/post/ssvxmrdpklhsrqlgrzas@forum.d
 
 - Messages, when selected, the recently added _Search Results_ category could not be emptied.
 - Highlighter, `q"()"`, `q"[]"`, `q"<>"`, `q"{}>"` strings highlighting was broken.
+- HTML export, the dialog proposed to open a file, not to save one.
 
 # v3.9.8
 

src/u_main.pas

@@ -2603,7 +2603,7 @@ begin
     exit;
   exp := TSynExporterHTML.Create(nil);
   try
-    with TOpenDialog.Create(nil) do
+    with TSaveDialog.Create(nil) do
     try
       if Execute then
       begin