wayland: Always set the last incoming clipboard seat when setting clipboard data

Otherwise, the clipboard will report having no or old data until events are pumped.

Fixes the automated clipboard tests.

src/video/wayland/SDL_waylandclipboard.c

@@ -40,6 +40,8 @@ bool Wayland_SetClipboardData(SDL_VideoDevice *_this)
         seat = wl_container_of(video_data->seat_list.next, seat, link);
     }
 
+    video_data->last_incoming_data_offer_seat = seat;
+
     if (seat && seat->data_device) {
         SDL_WaylandDataDevice *data_device = seat->data_device;
 
@@ -119,6 +121,8 @@ bool Wayland_SetPrimarySelectionText(SDL_VideoDevice *_this, const char *text)
         seat = wl_container_of(video_data->seat_list.next, seat, link);
     }
 
+    video_data->last_incoming_primary_selection_seat = seat;
+
     if (seat && seat->primary_selection_device) {
         SDL_WaylandPrimarySelectionDevice *primary_selection_device = seat->primary_selection_device;
         if (text[0] != '\0') {