fix NPA in IMConversationManagerPrivate::newMessage()

NPA causing crash when IMConversationManagerPrivate::newMessage()
is called with a non existing callId.

Change-Id: I5c1fd7e8e56b7bd3b2feb72281fddaf90442c649
Reviewed-by: Nicolas Jäger <nicolas.jager@savoirfairelinux.com>

src/media/text.cpp

@@ -143,7 +143,7 @@ void IMConversationManagerPrivate::newMessage(const QString& callId, const QStri
    Q_UNUSED(from)
 
    auto call = CallModel::instance().getCall(callId);
-   if (!call and !call->peerContactMethod()) {
+   if (!call or !call->peerContactMethod()) {
       return;
    }