fix bug when Msg ID is not set in DBC Editing Window

dbcmaineditor.cpp

@@ -382,7 +382,9 @@ void DBCMainEditor::onCellClickedMessage(int row, int col)
 {
     if (col == 3) //3 is the signals field. If clicked we go to the signals dialog
     {
-        QString idString = ui->MessagesTable->item(row, 0)->text();
+        QTableWidgetItem* msg = ui->MessagesTable->item(row, 0);
+        if(msg) {
+            QString idString = msg->text();
             DBC_MESSAGE *message = dbcFile->messageHandler->findMsgByID(Utility::ParseStringToNum(idString));
             sigEditor->setMessageRef(message);
             sigEditor->setFileIdx(fileIdx);
@@ -394,6 +396,7 @@ void DBCMainEditor::onCellClickedMessage(int row, int col)
             inhibitCellChanged = false;
         }
     }
+}
 
 void DBCMainEditor::refreshNodesTable()
 {