Tbs: Fix error handling for the join call

Make sure to exit early from the case, when error occure on callIndex
validation.

Bug: 232902624
Bug: 233006618
Tag: #feature
Test: atest BluetoothInstrumentationTests
Merged-In: I080c7fa0baea529f40c3812c10245fd3dbd14100
Change-Id: I080c7fa0baea529f40c3812c10245fd3dbd14100
(cherry picked from commit 8044f0b8)