Prevent crash when a Browsable player has an empty root

Bug: 110051940
Test: runtest bluetooth -c
com.android.bluetooth.avrcp.BrowserPlayerWrapperTest

Change-Id: I2d6db2814f3ea61e95e0a1cc8417274f103af5de
(cherry picked from commit acdf7d6bc28bdda01a3918772d0082fa75bc91c5)
2 files changed