Fix crash on connected devices settings

If disconnected bluetooth devices didn't exist in
recent devices, the index will return -1. Our condition
didn't check this situation, the IndexOutOfBoundsException
will throw when this case happens.

This CL adds the condition to check whether index is over
than or equal 0 to fix IndexOutOfBoundsException.

Bug: 173059077
Test: make -j42 RunSettingsRoboTests
Change-Id: Id93f4cb6bded83540045c5e8c21c6f6122a39fed