If a parse or reparse operation fails, the corresponding translation
unit is "not intact" anymore and further job requests for that
translation unit will be silently discarded without notifying the
plugin. This is especially problematic when the plugin expects/waits
(for) a certain message.

A parse/reparse can fail due to e.g. an invalid commandline or an
internal crash.

In such a case, ensure to send some dummy results.

Task-number: QTCREATORBUG-18864
Change-Id: Ida9b8066fd55e64027a9b0d8bd5cf365b16a7356
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>