wayland: Use the implicit grab serial when clearing the clipboard

Some compositors won't clear the selection without a valid serial.

src/video/wayland/SDL_waylanddatamanager.c

@@ -632,7 +632,7 @@ bool Wayland_data_device_clear_selection(SDL_WaylandDataDevice *data_device)
     if (!data_device || !data_device->data_device) {
         result = SDL_SetError("Invalid Data Device");
     } else if (data_device->selection_source) {
-        wl_data_device_set_selection(data_device->data_device, NULL, 0);
+        wl_data_device_set_selection(data_device->data_device, NULL, data_device->seat->last_implicit_grab_serial);
         Wayland_data_source_destroy(data_device->selection_source);
         data_device->selection_source = NULL;
     }
@@ -647,7 +647,7 @@ bool Wayland_primary_selection_device_clear_selection(SDL_WaylandPrimarySelectio
         result = SDL_SetError("Invalid Primary Selection Device");
     } else if (primary_selection_device->selection_source) {
         zwp_primary_selection_device_v1_set_selection(primary_selection_device->primary_selection_device,
-                                                      NULL, 0);
+                                                      NULL, primary_selection_device->seat->last_implicit_grab_serial);
         Wayland_primary_selection_source_destroy(primary_selection_device->selection_source);
         primary_selection_device->selection_source = NULL;
     }