qml: fix refactoring to separate component

* avoid extra spaces
* warn about existing files

Fixes: QTCREATORBUG-21091
Change-Id: Ic9ed4444bd028455e1b2d1755e6c43f352dfd5e3
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/plugins/qmljseditor/qmljscomponentnamedialog.cpp

@@ -168,5 +168,8 @@ QString ComponentNameDialog::isValid() const
     if (!ui->pathEdit->isValid())
         return tr("Invalid path");
 
+    if (QDir(ui->pathEdit->path()).exists(compName + u".qml"))
+        return tr("Component exists already");
+
     return QString();
 }