scm: mercurial: fix exception operation in adapter "summary" method (#4455).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@4876 e93f8b46-1217-0410-a6f0-8f06a7374b81

lib/redmine/scm/adapters/mercurial_adapter.rb

@@ -110,10 +110,17 @@ module Redmine
         end
 
         def summary
-          @summary ||= hg 'rhsummary' do |io|
-            ActiveSupport::XmlMini.parse(io.read)['rhsummary']
+          return @summary if @summary 
+          doc = nil
+          hg 'rhsummary' do |io|
+            output = io.read
+            begin
+              doc = ActiveSupport::XmlMini.parse(output)['rhsummary']
+            rescue
             end
           end
+          @summary = doc
+        end
         private :summary
 
         def entries(path=nil, identifier=nil)