shm_lock_test: add nil check

Fixes: #6164
Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

libpod/lock/shm/shm_lock_test.go

@@ -76,6 +76,7 @@ func TestCreateNewSHMBadSizeRoundsUp(t *testing.T) {
 	// Odd number, not a power of 2, should never be a word size on a system
 	lock, err := CreateSHMLock("/test1", 7)
 	assert.NoError(t, err)
+	assert.NotNil(t, lock)
 
 	assert.Equal(t, lock.GetMaxLocks(), BitmapSize)