[FIX] sap.ui.unified.ShellOverlay: Fix keyboard handling (Tabchain,
Close Button)

Change-Id: Icd977bcfd1c0b7f01eacad01ac42b526505b097b
CR-Id: 012006153200015668012014
Merge "[FIX] sap.ui.unified.ShellOverlay: Fix keyboard handling (Tabchain, Close Button)" into rel-1.26