Spotifyd MPRIS freezes Wingpanel

## What Happened
When opening spotifyd with mpris enabled, wingpanel freezes completely (and also the rest of the wm, cant move nor select windows, only by alt-tabbing). If I play a song through spotifyd, or if I kill spotifyd, wingpanel resumes normal functions. Monitoring wingpanel through terminal while frozen doesn't output any lines of errors (literally none) but when a song is played, and normal function is restored, Critical gtk warnings are issued. See log for those errors.
When opened without mpris this does not happen.

## Expected Behavior
Opening spotifyd without playing a song should not interfere with the responsiveness of wingpanel

## Steps to Reproduce

1. Run spotifyd with mpris enabled
2. Do not play any song
3. Click in sound or any other indicator in wingpanel, the panel (and sometimes wm gala) is freezed
4. Through some client start playing songs on spotify
5. Wingpanel should start working again, without rebooting itself.

### Logs
```
(wingpanel:5919): GLib-CRITICAL **: 16:45:36.091: g_hash_table_contains: assertion 'hash_table != NULL' failed

(wingpanel:5919): GLib-CRITICAL **: 16:45:36.091: g_hash_table_contains: assertion 'hash_table != NULL' failed

(wingpanel:5919): GLib-CRITICAL **: 16:45:36.091: g_hash_table_contains: assertion 'hash_table != NULL' failed

** (wingpanel:5919): CRITICAL **: 16:45:36.183: session_widgets_userbox_update_state: assertion 'self != NULL' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.225: gtk_widget_get_allocation: assertion 'GTK_IS_WIDGET (widget)' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.225: gtk_widget_get_parent: assertion 'GTK_IS_WIDGET (widget)' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.225: gtk_widget_get_allocation: assertion 'GTK_IS_WIDGET (widget)' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.226: gtk_widget_get_allocation: assertion 'GTK_IS_WIDGET (widget)' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.226: gtk_widget_get_parent: assertion 'GTK_IS_WIDGET (widget)' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.226: gtk_widget_get_allocation: assertion 'GTK_IS_WIDGET (widget)' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.227: gtk_widget_get_allocation: assertion 'GTK_IS_WIDGET (widget)' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.227: gtk_widget_get_parent: assertion 'GTK_IS_WIDGET (widget)' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.227: gtk_widget_get_allocation: assertion 'GTK_IS_WIDGET (widget)' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.227: gtk_widget_get_allocation: assertion 'GTK_IS_WIDGET (widget)' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.227: gtk_widget_get_parent: assertion 'GTK_IS_WIDGET (widget)' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.227: gtk_widget_get_allocation: assertion 'GTK_IS_WIDGET (widget)' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.227: gtk_widget_get_allocation: assertion 'GTK_IS_WIDGET (widget)' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.227: gtk_widget_get_parent: assertion 'GTK_IS_WIDGET (widget)' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.227: gtk_widget_get_allocation: assertion 'GTK_IS_WIDGET (widget)' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.230: gtk_widget_get_allocation: assertion 'GTK_IS_WIDGET (widget)' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.230: gtk_widget_get_parent: assertion 'GTK_IS_WIDGET (widget)' failed

(wingpanel:5919): Gtk-CRITICAL **: 16:45:36.230: gtk_widget_get_allocation: assertion 'GTK_IS_WIDGET (widget)' failed
```

## Platform Information
* Elementary OS 5.1.7 Hera
* Spotifyd version 0.3.0 (from releases in the github)
* Intel I3-5010U 2.1 GHz - 8 GB RAM - Intel HD Graphics 5500 (rev 09)
* Using elementary-tweaks (in case this is relevant)