virDomainMomentAssignDef: Simplify error handling
virDomainMomentAssignDef: Simplify error handling

Remove error handling from the call to 'virDomainMomentObjNew' as it
can't return NULL and replace 'virHashAddEntry' by 'g_hash_table_insert'
as we've already checked that snapshot with such name doesn't exist in
the hash table. This removes handling for two impossible errors.

Signed-off-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

crobinso/libvirt,jfehlig/libvirt,libvirt/libvirt,zippy2/libvirt,olafhering/libvirt,jfehlig/libvirt,zippy2/libvirt,crobinso/libvirt,libvirt/libvirt,olafhering/libvirt,libvirt/libvirt,jfehlig/libvirt,olafhering/libvirt,jfehlig/libvirt,zippy2/libvirt,crobinso/libvirt,olafhering/libvirt,zippy2/libvirt,libvirt/libvirt,crobinso/libvirt