fix markup formatting edge case

lib/gollum/markup.rb

@@ -179,6 +179,8 @@ module Gollum
     #   if it is not.
     def process_image_tag(tag)
       parts = tag.split('|')
+      return if parts.size.zero?
+
       name  = parts[0].strip
       path  = if file = find_file(name)
         ::File.join @wiki.base_path, file.path
@@ -267,6 +269,8 @@ module Gollum
     #   if it is not.
     def process_file_link_tag(tag)
       parts = tag.split('|')
+      return if parts.size.zero?
+
       name  = parts[0].strip
       path  = parts[1] && parts[1].strip
       path  = if path && file = find_file(path)

test/test_markup.rb

@@ -446,6 +446,18 @@ context "Markup" do
     compare(content, output, 'org')
   end
 
+  test "short double links" do
+    content = "a [[b]] c"
+    output  = %(<p class="title">a <a class="internal absent" href="/b">b</a> c</p>)
+    compare(content, output, 'org')
+  end
+
+  test "double linked pipe" do
+    content = "a [[|]] b"
+    output  = %(<p class="title">a <a class="internal absent" href="/"></a> b</p>)
+    compare(content, output, 'org')
+  end
+
   #########################################################################
   #
   # TeX