Ensure asio::streambuf's internal pointers are updated correctly after

the data has been modified using std::streambuf member functions.

Author: chriskohlhoff

asio/include/asio/basic_streambuf.hpp

@@ -236,6 +236,8 @@ class basic_streambuf
    */
   void consume(std::size_t n)
   {
+    if (egptr() < pptr())
+      setg(&buffer_[0], gptr(), pptr());
     if (gptr() + n > pptr())
       n = pptr() - gptr();
     gbump(static_cast<int>(n));