Prevent application crash

When the last file was closed the new file was not grabbing focus, and when switching back to the application the current editor was null. This forces focus on the new file and adds an additional check to prevent any future issues. Closes #749

Author: dail8859

src/NotepadNext/dialogs/MainWindow.cpp

@@ -960,7 +960,8 @@ void MainWindow::newFile()
         }
 
         if (canUseName) {
-            app->getEditorManager()->createEditor(newFileName);
+            ScintillaNext *editor = app->getEditorManager()->createEditor(newFileName);
+            editor->grabFocus();
             break;
         }
     }
@@ -1886,8 +1887,12 @@ void MainWindow::focusIn()
 {
     qInfo(Q_FUNC_INFO);
 
-    if (checkFileForModification(currentEditor())) {
-        updateGui(currentEditor());
+    ScintillaNext *editor = currentEditor();
+
+    if (editor) {
+        if (checkFileForModification(currentEditor())) {
+            updateGui(currentEditor());
+        }
     }
 }