Fix OPP comparison

isBluetoothShareUri_correctlyCheckUri (under
com.android.bluetooth.opp.BluetoothOppUtilityTest) is failing
on null input due to an incorrect comparison in
isBluetoothShareUri.  Change the comparison to one which can
cope with null input.

Bug: 257190999
Test: atest: BluetoothOppUtilityTest
Tag: #security
Ignore-AOSP-First: Security
Change-Id: Ia6a08e7092c2084e1816b782317c13254e78719b
(cherry picked from commit 90dc6fcdcba6c0c2b0f9bdaad28457a81c9af4ba)
Merged-In: Ia6a08e7092c2084e1816b782317c13254e78719b