qemu: Check for job being set when getting iothread stats
qemu: Check for job being set when getting iothread stats

The qemuDomainGetStatsIOThread() accesses the monitor by calling
qemuDomainGetIOThreadsMon(). And it's also marked as "need
monitor" in qemuDomainGetStatsWorkers[]. However, it's not
checking if acquiring job was successful.

Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>
Reviewed-by: Jonathon Jongsma <c7254805a17bd5c41e24c3a278fcbf3afcdfb0fa@redhat.com>

jardasgit/libvirt,jardasgit/libvirt,olafhering/libvirt,nertpinx/libvirt,zippy2/libvirt,libvirt/libvirt,fabianfreyer/libvirt,crobinso/libvirt,olafhering/libvirt,jfehlig/libvirt,nertpinx/libvirt,zippy2/libvirt,fabianfreyer/libvirt,crobinso/libvirt,crobinso/libvirt,jfehlig/libvirt,libvirt/libvirt,libvirt/libvirt,jardasgit/libvirt,zippy2/libvirt,fabianfreyer/libvirt,olafhering/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,jfehlig/libvirt,crobinso/libvirt,jardasgit/libvirt,olafhering/libvirt,jfehlig/libvirt,zippy2/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,libvirt/libvirt,nertpinx/libvirt,jardasgit/libvirt