Fix segv when switching from a call that was previously hungup.

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@16432 d0543943-73ff-0310-b7d9-9358b9ac24b2

fscomm/mainwindow.cpp

@@ -211,7 +211,9 @@ void MainWindow::callTableDoubleClick(QTableWidgetItem *item)
         return;
     }
     ui->hangupBtn->setEnabled(true);
-    lastCall.data()->setActive(false);
+    /* Last call was hungup and we are switching */
+    if (!lastCall.isNull())
+        lastCall.data()->setActive(false);
     call.data()->setActive(true);
 }