widget: Disconnect GtkSettings signals in destructor

This fixes a crash when the cursor blink settings are modified
after a terminal exits.

#77

src/vte.cc

@@ -8177,10 +8177,6 @@ Terminal::~Terminal()
 		g_object_unref(m_vadjustment);
 	}
 
-        g_signal_handlers_disconnect_matched (gtk_widget_get_settings(m_widget), G_SIGNAL_MATCH_DATA,
-                                              0, 0, NULL, NULL,
-                                              this);
-
         /* Update rects */
         g_array_free(m_update_rects, TRUE /* free segment */);
 }

src/widget.cc

@@ -103,6 +103,11 @@ Widget::Widget(VteTerminal* t) noexcept :
 
 Widget::~Widget() noexcept
 {
+        g_signal_handlers_disconnect_matched(gtk_widget_get_settings(m_widget),
+                                             G_SIGNAL_MATCH_DATA,
+                                             0, 0, NULL, NULL,
+                                             this);
+
         m_widget = nullptr;
 
         m_terminal->~Terminal();