force the offset to be calculated first to avoid confusing MSVC's checked iterators references zaphoyd#342

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Author: zaphoyd

websocketpp/http/impl/request.hpp

@@ -127,7 +127,7 @@ inline size_t request::consume(const char *buf, size_t len) {
             }
         }
 
-        begin = end+sizeof(header_delimiter)-1;
+        begin = end+(sizeof(header_delimiter)-1);
     }
 }