ProjectManagerPlugin: fix crash when no kits are found

I found this bug in a live session of Debian. I used the appimage, and
did not understand why the app crashed.

I manged to trace it down in a Win10 installation, that uses mingw
(which is a pain to debug, as it did not catch the exception, and
debugging loading takes about a minute).

Anyway, when no kits are available, at startup the combo box of the kits
will be set to 0, and will de-reference. Its actually an out of boundery
- we try to get element "0" when we have no elements. Just did an if,
and code no longer crashes.

Doing a rescan should be done as a first step - see https://github.com/
/issues/25

Author: diegoiast

src/plugins/ProjectManager/ProjectManagerPlg.cpp

@@ -583,6 +583,10 @@ void ProjectManagerPlugin::on_client_merged(qmdiHost *host) {
 
     gui->kitComboBox->setModel(kitsModel);
     connect(gui->kitComboBox, &QComboBox::activated, gui->kitComboBox, [this](int newIndex) {
+        if (kitsModel->rowCount() <= newIndex) {
+            qDebug() << "kitComboBox: No kits found, or wrong kit definted.";
+            return;
+        }
         auto kit = kitsModel->getKit(newIndex);
         auto tooltip = QString("%1\n%2").arg(QString::fromStdString(kit.name),
                                              QString::fromStdString(kit.filePath));