vtest: destroy renderer in no-fork mode

Make sure the next renderer is a cleaned up one.

Reviewed-by: Jakob Bornecrantz <jakob@collabora.com>
Signed-off-by: Jakob Bornecrantz <jakob@collabora.com>

vtest/vtest_server.c

@@ -219,6 +219,7 @@ start:
       }
     } else {
       run_renderer(in_fd, out_fd);
+      vtest_destroy_renderer();
       if (loop)
          goto restart;
     }