Fix situations when request's job is not set

Fix situations when request's job is not set

It is a good practice to check if pointer is not nil, before
dereferencing it. Verification if Job field of request is set
in closeRequest is such situation.

It is not an error situation if Worker state transition:
RUN->MAINTENANCE or RUN->FAIL happen and a request's is not run
by any Job. It can occur e.g. when worker is already booked for
a Job (in RUN state) and creation of Job is not yet completed
or failed.

Change-Id: Ib1790fdaab293b9478dc67f86b69f04a6808c50b
Signed-off-by: Lukasz Wojciechowski <l.wojciechow@partner.samsung.com>