engine: Fix coverity issue

CID 1223221 (#1 of 1): Dereference null return value (NULL_RETURNS)
dereference: Dereferencing a pointer that might be null task when
calling logAndFailTaskOfCommandWithEmptyVdsmId

Change-Id: Iec7dd5de85faa7c44a29aca85a31a41b7ac1f87a
Signed-off-by: Moti Asayag <masayag@redhat.com>