Add a regression test for PR 276191.

The bug isn't fusefs-specific, but this is the easiest way to reproduce
it.

PR: 276191
MFC with: bdb46c21a3e68d4395d6e0b6a205187e655532b0
Differential Revision: https://reviews.freebsd.org/D43446
Reviewed by: kib

(cherry picked from commit 6b1c534927ad47e9b0dd8be1a39f56c3ea813d44)