zink: only update framebuffer object during swapchain update if framebuffer exists

otherwise this might be randomly creating an unused framebuffer for dynamic render

cc: mesa-stable

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20584>

src/gallium/drivers/zink/zink_render_pass.c

@@ -835,7 +835,8 @@ zink_render_update_swapchain(struct zink_context *ctx)
       zink_kopper_fixup_depth_buffer(ctx);
       if (ctx->fb_state.width != old_w || ctx->fb_state.height != old_h)
          ctx->scissor_changed = true;
-      zink_update_framebuffer_state(ctx);
+      if (ctx->framebuffer)
+         zink_update_framebuffer_state(ctx);
       ctx->swapchain_size.width = ctx->swapchain_size.height = 0;
    }
 }