plug-ins: Try harder to export an image from darktable

Before there wouldn't be any intermediate file being written when
darktable sees more than one XMP file. Now the first image in its
temporary database gets exported.

plug-ins/file-darktable/export-on-exit.lua

@@ -43,8 +43,8 @@ local export_filename = dt.preferences.read("export_on_exit", "export_filename",
 dt.register_event("exit", function()
   -- safegurad against someone using this with their library containing 50k images
   if #dt.database > 1 then
-    dt.print_error("too many images, not exporting")
-    return
+    dt.print_error("too many images, only exporting the first")
+--     return
   end
 
   -- change the view first to force writing of the history stack
@@ -57,6 +57,7 @@ dt.register_event("exit", function()
   for _, image in ipairs(dt.database) do
     dt.print_error("exporting `"..tostring(image).."' to `"..export_filename.."'")
     format:write_image(image, export_filename)
+    break -- only export one image. see above for the reason
   end
 end)