Fix segfaults when add to graphing window for signal not found in DBC

mainwindow.cpp

@@ -535,6 +535,7 @@ void MainWindow::setupAddToNewGraph()
     setupSendToLatestGraphWindow(); //then call the other function to finish
 }
 
+
 void MainWindow::setupSendToLatestGraphWindow()
 {
     if (!lastGraphingWindow) showGraphingWindow();
@@ -542,7 +543,11 @@ void MainWindow::setupSendToLatestGraphWindow()
     QString signalName = getSignalNameFromPosition(contextMenuPosition);
     param.ID = getMessageIDFromPosition(contextMenuPosition);
     DBC_MESSAGE *msg = dbcHandler->findMessageForFilter(param.ID, nullptr);
+    if(msg)
+    {
         DBC_SIGNAL *sig = msg->sigHandler->findSignalByName(signalName);
+        if(sig)
+        {
             param.associatedSignal = sig;
             param.bias = sig->bias;
             param.intelFormat = sig->intelByteOrder;
@@ -561,7 +566,22 @@ void MainWindow::setupSendToLatestGraphWindow()
 
             lastGraphingWindow->createGraph(param); //add the new graph to the window
         }
-
+        else
+        {
+            QMessageBox msgbox;
+            QString boxmsg = "Cannot find ID 0x" + QStringLiteral("%1").arg(param.ID, 3, 16, QLatin1Char('0')) + " in DBC message " + msg->name + ". Not adding graph.";
+            msgbox.setText(boxmsg);
+            msgbox.exec();
+        }
+    }
+    else
+    {
+        QMessageBox msgbox;
+        QString boxmsg = "Cannot find ID 0x" + QStringLiteral("%1").arg(param.ID, 3, 16, QLatin1Char('0')) + " in DBC file(s). Not adding graph.";
+        msgbox.setText(boxmsg);
+        msgbox.exec();
+    }
+}
 void MainWindow::interpretToggled(bool state)
 {
     model->setInterpretMode(state);