sipcall: close audio thread when call is finished

checkAudio must be called to close audio threads when a call is
closed.

Change-Id: Iccfdccee9bd9dab2226a2092cf62e9ca225cf2ef

src/sip/sipcall.cpp

@@ -749,6 +749,7 @@ SIPCall::onClosed()
             auto& call = *shared;
             Manager::instance().peerHungupCall(call);
             call.removeCall();
+            Manager::instance().checkAudio();
         }
     });
 }