Ensure asio::streambuf's internal pointers are updated correctly after
the data has been modified using std::streambuf member functions.

asio/include/asio/basic_streambuf.hpp

diff --git a/asio/include/asio/basic_streambuf.hpp b/asio/include/asio/basic_streambuf.hpp
index 17157da..f8ba737 100644
--- a/asio/include/asio/basic_streambuf.hpp
+++ b/asio/include/asio/basic_streambuf.hpp
@@ -236,6 +236,8 @@
    */
   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));