Call handler only when reader is without errors.

lib/c/labcomm_decoder.c

@@ -259,12 +259,14 @@ static void call_handler(void *value, void *context)
 {
   struct call_handler_context *wrap = context;
 
+  if (wrap->reader->error >= 0) {
     labcomm_reader_start(wrap->reader, wrap->reader->action_context,
 			 wrap->local_index, wrap->remote_index, wrap->signature,
 			 value);
     wrap->handler(value, wrap->context);
     labcomm_reader_end(wrap->reader, wrap->reader->action_context);
   }
+}
 
 static void reader_alloc(struct labcomm_decoder *d)
 {