Optimize Document::DATE_FILENAME_MATCHER to match valid filenames (#7292)

Merge pull request 7292

lib/jekyll/document.rb

@@ -12,7 +12,7 @@ module Jekyll
 
     YAML_FRONT_MATTER_REGEXP = %r!\A(---\s*\n.*?\n?)^((---|\.\.\.)\s*$\n?)!m.freeze
     DATELESS_FILENAME_MATCHER = %r!^(?:.+/)*(.*)(\.[^.]+)$!.freeze
-    DATE_FILENAME_MATCHER = %r!^(?:.+/)*(\d{2,4}-\d{1,2}-\d{1,2})-(.*)(\.[^.]+)$!.freeze
+    DATE_FILENAME_MATCHER = %r!^(?>.+/)*?(\d{2,4}-\d{1,2}-\d{1,2})-([^/]*)(\.[^.]+)$!.freeze
 
     # Create a new Document.
     #

test/source/_posts/2013-03-19-not-a-post/dubious.markdown

@@ -0,0 +1,6 @@
+---
+title: What Am I?
+---
+
+I am not a post.
+Am I a document then..?

test/test_site.rb

@@ -95,7 +95,7 @@ class TestSite < JekyllUnitTest
   context "creating sites" do
     setup do
       @site = Site.new(site_configuration)
-      @num_invalid_posts = 5
+      @num_invalid_posts = 6
     end
 
     teardown do