Quality of Life Was Not Negatively Impacted By the Addition of Lenalidomide to R-CHOP Chemotherapy (R2-CHOP) Compared with Placebo Plus R-CHOP Chemotherapy in Patients with Previously Untreated Activated B-Cell (ABC)-Type Diffuse Large B-Cell Lymphoma (DLBCL): Health-Related Quality of Life (HRQoL) Analysis of the International Robust Study