Ensure one cannot save DBC files with blank message and signal names,

fix up some warnings.

dbc/dbcsignaleditor.cpp

@@ -156,7 +156,8 @@ DBCSignalEditor::DBCSignalEditor(QWidget *parent) :
             [=]()
             {
                 if (currentSignal == NULL) return;
-                currentSignal->name = ui->txtName->text().simplified().replace(' ', '_');
+                QString tempNameStr = ui->txtName->text().simplified().replace(' ', '_');
+                if (tempNameStr.length() > 0) currentSignal->name = tempNameStr;
                 //need to update the list too.
                 ui->signalsList->currentItem()->setText(currentSignal->name);
             });