Fixed notification trying to set icon from invalid .desktop file

src/notification/notification.vala

@@ -440,9 +440,12 @@ namespace SwayNotificationCenter {
                 if (param.desktop_entry != null) {
                     string entry = param.desktop_entry;
                     entry = entry.replace (".desktop", "");
-                    var entry_info = new DesktopAppInfo (
+                    DesktopAppInfo entry_info = new DesktopAppInfo (
                         "%s.desktop".printf (entry));
-                    icon = entry_info.get_icon ();
+                    // Checks if the .desktop file actually exists or not
+                    if (entry_info is DesktopAppInfo) {
+                        icon = entry_info.get_icon ();
+                    }
                 }
                 if (icon != null) {
                     img.set_from_gicon (icon, icon_size);