Change default HTTP response error code to 426

Changes default HTTP response error code when no http_handler is
defined from 500/Internal Server Error to 426/Upgrade Required

changelog.md

@@ -1,4 +1,6 @@
 HEAD
+- Changes default HTTP response error code when no http_handler is defined from
+  500/Internal Server Error to 426/Upgrade Required
 - Removes timezone from logger timestamp to work around issues with the Windows
   implimentation of strftime. Thank you breyed for testing and code. #257
 - Switches integer literals to char literals to improve VCPP compatibility.

websocketpp/impl/connection_impl.hpp

@@ -989,6 +989,8 @@ bool connection<config>::process_handshake_request() {
         
         if (m_http_handler) {
             m_http_handler(m_connection_hdl);
+        } else {
+            set_status(http::status_code::upgrade_required);
         }
 
         return true;