Revert "check for `read_only?` first before seeing if request is disallowed"

This reverts commit 91075c82.

lib/gitlab/middleware/read_only.rb

@@ -14,7 +14,7 @@ module Gitlab
         @env = env
         @route_hash = nil
 
-        if Gitlab::Database.read_only? && disallowed_request?
+        if disallowed_request? && Gitlab::Database.read_only?
           Rails.logger.debug('GitLab ReadOnly: preventing possible non read-only operation')
           error_message = 'You cannot do writing operations on a read-only GitLab instance'