trickle handler daemon: mark message as handled even if handler returns error.

This is because errors in general are non-recoverable,
and we'll end up retrying infinitely.
If an error actually is recoverable, exit().

sched/trickle_handler.cpp

@@ -67,9 +67,12 @@ bool do_trickle_scan() {
         }
         retval = handle_trickle(mfh);
         if (!retval) {
+            log_messages.printf(MSG_CRITICAL,
+                "handle_trickle(): %s", boincerror(retval)
+            );
+        }
         mfh.handled = true;
         mfh.update();
-        }
         found = true;
     }
     return found;