Fix missing check for error code after header is parsed:

The missing error check leads to completely ignoring the body limit,
as the body limit is compared to the "Content-Length" header inside
the "finish_header" method.

closes #2201

include/boost/beast/http/impl/basic_parser.ipp

@@ -164,6 +164,8 @@ loop:
             goto done;
         }
         finish_header(ec, is_request{});
+        if(ec)
+            goto done;
         break;
 
     case state::body0: