Fix crash bug when update shortcuts

Setting dynamic shortcuts will get exception when DocumentsUI
does not show on launcher. Because shourtcuts only work when it
shows on launcher, do not set shortcuts when it does not show on
launcher to fix this bug.

Fix: 122278185
Test: atest DocumentsUITests
Change-Id: I504ecbbafd1f78a90a269ec8b648a3f75e94a916