Fix uncaught error when saving a new playlist

Author: zeebok

src/Application.vala

@@ -151,7 +151,8 @@ public class Music.Application : Gtk.Application {
                 continue;
             }
             else if (PlaylistObject.is_playlist (file)) {
-                PlaylistObject playlist = new PlaylistObject.with_file (file);
+                PlaylistObject playlist = new PlaylistObject (file);
+                playlist.load_playlist ();
 
                 foreach (File playlist_file in playlist.get_uri_list ()) {
                     elements += playlist_file;

src/PlaybackManager.vala

@@ -419,7 +419,7 @@ public class Music.PlaybackManager : Object {
                 File? file;
                 file = save_dialog.save.end (res);
 
-                PlaylistObject playlist = new PlaylistObject.with_file (file);
+                PlaylistObject playlist = new PlaylistObject (file);
                 playlist.save_playlist (queue_liststore);
             } catch (Error err) {
                 if (err.matches (Gtk.DialogError.quark (), Gtk.DialogError.DISMISSED)) {

src/PlaylistObject.vala

@@ -7,17 +7,10 @@ public class Music.PlaylistObject : Object {
     public File playlist_file { get; construct; }
     private File[] uri_list = {};
 
-    public PlaylistObject () {}
-
-
-    public PlaylistObject.with_file (File playlist) {
+    public PlaylistObject (File playlist) {
         Object (playlist_file: playlist);
     }
 
-    construct {
-        load_playlist (playlist_file);
-    }
-
     public static bool is_playlist (File playlist) {
         FileInfo info;
 
@@ -43,8 +36,8 @@ public class Music.PlaylistObject : Object {
         return uri_list;
     }
 
-    private void load_playlist (File playlist) {
-        FileInputStream fis = playlist.read ();
+    public void load_playlist () requires (playlist_file != null) {
+        FileInputStream fis = playlist_file.read ();
         DataInputStream dis = new DataInputStream (fis);
         string current_line;
 
@@ -61,7 +54,7 @@ public class Music.PlaylistObject : Object {
         }
     }
 
-    public void save_playlist (ListStore queue) {
+    public void save_playlist (ListStore queue) requires (playlist_file != null) {
         FileOutputStream fos = playlist_file.replace (null, false, GLib.FileCreateFlags.REPLACE_DESTINATION);
         DataOutputStream dos = new DataOutputStream (fos);