zink: return false on failure

We do this in the other pipe_buffer_map_range failure case, so it makes
sense that we need to do it here as well. If we don't, we'll end up
taking a crash in the check_query_results function, which will
dereference that pointer.

We also need to unmap the buffer if we fail, otherwise we'll leak.

CID: 1475925

Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12559>

src/gallium/drivers/zink/zink_query.c

@@ -469,6 +469,8 @@ get_query_result(struct pipe_context *pctx,
          if (!xfb_results) {
             if (wait)
                debug_printf("zink: xfb qbo read failed!");
+            pipe_buffer_unmap(pctx, xfer);
+            return false;
          }
       }
       check_query_results(query, result, is_timestamp ? 1 : qbo->num_results, results, xfb_results);