+ split file extension from descriptive text of file format to avoid that invalid translation breaks file dialog

+ add method to make image view unclosable for user
+ fix possible crash in MeshAlgorithm::GetMeshBorder
+ fix possible crash in MeshAlgorithm::ConnectLines

src/Gui/View3DInventor.cpp

@@ -450,7 +450,8 @@ void View3DInventor::print()
 
 void View3DInventor::printPdf()
 {
-    QString filename = FileDialog::getSaveFileName(this, tr("Export PDF"), QString(), tr("PDF file (*.pdf)"));
+    QString filename = FileDialog::getSaveFileName(this, tr("Export PDF"), QString(), 
+        QString::fromLatin1("%1 (*.pdf)").arg(tr("PDF file")));
     if (!filename.isEmpty()) {
         Gui::WaitCursor wc;
         QPrinter printer(QPrinter::ScreenResolution);