Always check if a Folder exists before accessing it

This kinds of bugs will be less frequent once we have non null by
default enabled in Flutter.

Fixes #164

lib/screens/settings_editors.dart

@@ -6,6 +6,7 @@ import 'package:gitjournal/core/notes_folder_fs.dart';
 import 'package:gitjournal/screens/settings_screen.dart';
 import 'package:gitjournal/screens/settings_widgets.dart';
 import 'package:gitjournal/settings.dart';
+import 'package:gitjournal/utils.dart';
 import 'package:gitjournal/widgets/folder_selection_dialog.dart';
 import 'package:gitjournal/widgets/pro_overlay.dart';
 
@@ -22,6 +23,15 @@ class SettingsEditorsScreenState extends State<SettingsEditorsScreen> {
         Settings.instance.journalEditordefaultNewNoteFolderSpec;
     if (defaultNewFolder.isEmpty) {
       defaultNewFolder = tr("rootFolder");
+    } else {
+      if (!folderWithSpecExists(context, defaultNewFolder)) {
+        setState(() {
+          defaultNewFolder = tr("rootFolder");
+
+          Settings.instance.journalEditordefaultNewNoteFolderSpec = "";
+          Settings.instance.save();
+        });
+      }
     }
 
     var body = ListView(children: <Widget>[

lib/screens/settings_images.dart

@@ -21,6 +21,12 @@ class SettingsImagesScreenState extends State<SettingsImagesScreen> {
     var folder = Provider.of<NotesFolderFS>(context)
         .getFolderWithSpec(settings.imageLocationSpec);
 
+    // If the Custom Folder specified no longer exists
+    if (settings.imageLocationSpec != "." && folder == null) {
+      Settings.instance.imageLocationSpec = ".";
+      Settings.instance.save();
+    }
+
     var sameFolder = tr("settings.images.currentFolder");
     var customFolder = tr("settings.images.customFolder");
 
@@ -72,15 +78,3 @@ class SettingsImagesScreenState extends State<SettingsImagesScreen> {
     );
   }
 }
-
-//
-// Options to expose
-// - Image Location
-//   - Note Directory
-//   - Custom Directory
-// Bool use relative path if possible
-// - Image FileName
-//   - Original Name
-//   - Note FileName + _num
-//   - Custom Name
-//

lib/screens/settings_screen.dart

@@ -134,6 +134,15 @@ class SettingsListState extends State<SettingsList> {
     var defaultNewFolder = Settings.instance.defaultNewNoteFolderSpec;
     if (defaultNewFolder.isEmpty) {
       defaultNewFolder = tr("rootFolder");
+    } else {
+      if (!folderWithSpecExists(context, defaultNewFolder)) {
+        setState(() {
+          defaultNewFolder = tr("rootFolder");
+
+          Settings.instance.defaultNewNoteFolderSpec = "";
+          Settings.instance.save();
+        });
+      }
     }
 
     return ListView(children: [

lib/utils.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 
 import 'package:package_info/package_info.dart';
+import 'package:provider/provider.dart';
 
 import 'package:gitjournal/core/notes_folder_fs.dart';
 import 'package:gitjournal/screens/note_editor.dart';
@@ -50,14 +51,16 @@ NotesFolderFS getFolderForEditor(
   EditorType editorType,
 ) {
   var spec = Settings.instance.defaultNewNoteFolderSpec;
-  var journalSpec = Settings.instance.journalEditordefaultNewNoteFolderSpec;
 
   switch (editorType) {
     case EditorType.Journal:
-      return rootFolder.getFolderWithSpec(journalSpec);
+      spec = Settings.instance.journalEditordefaultNewNoteFolderSpec;
+      break;
     default:
-      return rootFolder.getFolderWithSpec(spec);
+      break;
   }
+
+  return rootFolder.getFolderWithSpec(spec) ?? rootFolder;
 }
 
 Future<void> showAlertDialog(
@@ -68,3 +71,10 @@ Future<void> showAlertDialog(
   );
   return showDialog(context: context, builder: (context) => dialog);
 }
+
+bool folderWithSpecExists(BuildContext context, String spec) {
+  var stateContainer = Provider.of<StateContainer>(context, listen: false);
+  var rootFolder = stateContainer.appState.notesFolder;
+
+  return rootFolder.getFolderWithSpec(spec) != null;
+}