Removing the xJobExecutor.is() check from
SfxGlobalEvents_Impl::implts_notifyJobExecution was wrong, as
m_xJobExecutorListener was a WeakReference.  However, it appears there is no
good reason for the latter, so the situation can be corrected by turning it into
a plain Reference.

Change-Id: I5690d226b3e8fdd97f75a37502e600b460ec674c