fstest: fix upwrapping tests for bucket based remotes

TestIntegration/FsRmdirNotFound was failing on crypt wrapping a bucket based remote.

This was spotted by the integration tests.

fstest/fstests/fstests.go

@@ -335,7 +335,8 @@ func Run(t *testing.T, opt *Opt) {
 	// Return true if f (or any of the things it wraps) is bucket
 	// based but not at the root.
 	isBucketBasedButNotRoot := func(f fs.Fs) bool {
-		return fs.UnWrapFs(f).Features().BucketBased && strings.Contains(strings.Trim(f.Root(), "/"), "/")
+		f = fs.UnWrapFs(f)
+		return f.Features().BucketBased && strings.Contains(strings.Trim(f.Root(), "/"), "/")
 	}
 
 	// Initialise the remote