readall: put nostdout in outter layer

The previous code would fail to reset stdout after thread jobs are finshed.

Library/Homebrew/cmd/readall.rb

@@ -17,17 +17,19 @@ module Homebrew
       end
 
       failed = false
+      nostdout do
         workers = (0...Hardware::CPU.cores).map do
           Thread.new do
             begin
               while rb = ruby_files.pop(true)
-              nostdout { failed = true unless system RUBY_PATH, "-c", "-w", rb }
+                failed = true unless system RUBY_PATH, "-c", "-w", rb
               end
             rescue ThreadError # ignore empty queue error
             end
           end
         end
         workers.map(&:join)
+      end
       Homebrew.failed = failed
     end