ENHANCED: http_read_data/3: map syntax errors to status 400

If reading the data results in a syntax error we add context that causes
http_exception.pl to map the error to a HTTP 400 reply rather than HTTP 500.

Author: JanWielemaker

http_client.pl

@@ -242,7 +242,9 @@
 http_read_data(Fields, Data, QOptions) :-
     meta_options(is_meta, QOptions, Options),
     memberchk(input(In), Fields),
-    (   http_read_data(In, Fields, Data, Options)
+    (   catch(http_read_data(In, Fields, Data, Options),
+              error(Formal,_),
+              throw(error(Formal, context(_, in_http_request))))
     ->  true
     ;   throw(error(failed(http_read_data), _))
     ).