Don't reset default launcher if the user is not loaded

If the user is not loaded in ShortcutService, there is no need to reset
the current default launcher. This is to prevent any unnecessary file IO
when the default launcher changes.

Bug: 173614832
Test: atest com.android.server.pm.ShortcutManagerTest1
            com.android.server.pm.ShortcutManagerTest2
            com.android.server.pm.ShortcutManagerTest3
            com.android.server.pm.ShortcutManagerTest4
            com.android.server.pm.ShortcutManagerTest5
            com.android.server.pm.ShortcutManagerTest6
            com.android.server.pm.ShortcutManagerTest7
            com.android.server.pm.ShortcutManagerTest8
            com.android.server.pm.ShortcutManagerTest9
            com.android.server.pm.ShortcutManagerTest10
            com.android.server.pm.ShortcutManagerTest11
      atest CtsShortcutHostTestCases
      atest CtsShortcutManagerTestCases
Change-Id: Ic3bbb0f7b4d308bddbff1d586a8700388f317f6b