Assert that, for POLLIN received, there actually is data to be read

src/vdfp_pipe.c

@@ -473,17 +473,12 @@ vdp_bytes(struct vdp_ctx *ctx, enum vdp_action act, void **priv,
 				close_all(fds);
 				return (-1);
 			}
+			assert(nbytes > 0);
 			if (i == STDOUT_FILENO &&
 			    fds[i].revents & POLLHUP &&
 			    nbytes < obj->bufsz) {
 				act_bytes = VDP_END;
 			}
-			if (nbytes == 0) {
-				if (i == STDOUT_FILENO)
-					closefd(&fds[STDOUT_FILENO].fd);
-				else
-					closefd(&fds[STDERR_FILENO].fd);
-			}
 			if (i == STDOUT_FILENO) {
 				retval = VDP_bytes(ctx, act_bytes, state->buf,
 						   nbytes);