When handle_invite_replaces() was called, and either ast_bridge_impart()
failed or there was no bridge (because the channel we're picking up was
still ringing), chan_sip would leak a channel.

Thanks Matt and Corey for checking the bridge path.

ASTERISK-25226 #close

Change-Id: Ie736bb182170a73eef5bcef0ab0376f645c260c8