[FIX] sap.ui.core.Element: Ensure not to add 'null'-Delegates

Change-Id: Iaf4dbe25fe65bad714ce31bc5306173de6b1bb1c
(cherry picked from commit 0642ee3c1475bc28eb712166f4e47fbbcb953011)

Change-Id: Id4fb42ef936f9f985fe31ef4f42a6fac9cfff7eb
CR-Id: 012006153200015587402014
Merge "[FIX] sap.ui.core.Element: Ensure not to add 'null'-Delegates" into rel-1.26