Bug fixes on hangup when the call didn't exist

src/managerimpl.cpp

@@ -273,9 +273,12 @@ ManagerImpl::hangupCall (CALLID id)
 {
   ost::MutexLock m(_mutex);
   Call* call = getCall(id);
-  if (call == NULL && call->getState() != Call::Error) {
+  if (call == NULL) {
     return -1;
   }
+  if (call->getState() != Call::Error) { 
+    return -1; 
+  }
   int result = call->hangup();
   deleteCall(id);
   stopTone(); // stop tone, like a 700 error: number not found Not Found