Use correct title in og:title for pages with no title

Fixes #1098

app/helpers/title_helper.rb

@@ -5,7 +5,7 @@ module TitleHelper
     @coder ||= HTMLEntities.new
   end
 
-  def set_title(title = false)
+  def set_title(title = nil)
     if title
       @title = TitleHelper.coder.decode(title.gsub("<bdi>", "\u202a").gsub("</bdi>", "\u202c"))
       response.headers["X-Page-Title"] = URI.escape(t("layouts.project_name.title") + " | " + @title)

test/helpers/title_helper_test.rb

@@ -3,6 +3,10 @@ require "test_helper"
 
 class TitleHelperTest < ActionView::TestCase
   def test_set_title
+    set_title
+    assert_equal "OpenStreetMap", response.header["X-Page-Title"]
+    assert_nil @title
+
     set_title(nil)
     assert_equal "OpenStreetMap", response.header["X-Page-Title"]
     assert_nil @title