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: I61118f22577de7b975fb0df8dac8583e91f7b8c7
(cherry picked from commit c9b53b95)
Merged-In: I61118f22577de7b975fb0df8dac8583e91f7b8c7