Crash in markdown formatter causes ruby process to end (#16781).

Patch by Jens Krämer.

git-svn-id: http://svn.redmine.org/redmine/trunk@13122 e93f8b46-1217-0410-a6f0-8f06a7374b81

lib/redmine/wiki_formatting/markdown/formatter.rb

@@ -28,7 +28,7 @@ module Redmine
           unless link && link.starts_with?('/')
             css = 'external'
           end
-          content_tag('a', content.html_safe, :href => link, :title => title, :class => css)
+          content_tag('a', content.to_s.html_safe, :href => link, :title => title, :class => css)
         end
 
         def block_code(code, language)

test/unit/lib/redmine/wiki_formatting/markdown_formatter.rb

@@ -24,6 +24,18 @@ class Redmine::WikiFormatting::MarkdownFormatterTest < ActionView::TestCase
     @formatter = Redmine::WikiFormatting::Markdown::Formatter
   end
 
+  def test_syntax_error_in_image_reference_should_not_raise_exception
+    assert @formatter.new("!>[](foo.png)").to_html
+  end
+
+  # re-using the formatter after getting above error crashes the
+  # ruby interpreter. This seems to be related to
+  # https://github.com/vmg/redcarpet/issues/318
+  def test_should_not_crash_redcarpet_after_syntax_error
+    @formatter.new("!>[](foo.png)").to_html rescue nil
+    assert @formatter.new("![](foo.png)").to_html.present?
+  end
+
   def test_inline_style
     assert_equal "<p><strong>foo</strong></p>", @formatter.new("**foo**").to_html.strip
   end