rc: fix operations/stat with trailing /

Before this change using operations/stat with a remote pointing to a
dir with a trailing / would return a null output rather than the
correct info.

This was because the directory was not found with a trailing slash in
the directory listing.

Fixes #6817

fs/operations/lsjson.go

@@ -314,6 +314,9 @@ func StatJSON(ctx context.Context, fsrc fs.Fs, remote string, opt *ListJSONOpt)
 		}
 	}
 	// Must be a directory here
+	//
+	// Remove trailing / as rclone listings won't have them
+	remote = strings.TrimRight(remote, "/")
 	parent := path.Dir(remote)
 	if parent == "." || parent == "/" {
 		parent = ""

fs/operations/lsjson_test.go

@@ -292,6 +292,15 @@ func TestStatJSON(t *testing.T) {
 				Name:  "sub",
 				IsDir: true,
 			},
+		}, {
+			name:   "DirWithTrailingSlash",
+			remote: "sub/",
+			opt:    operations.ListJSONOpt{},
+			want: &operations.ListJSONItem{
+				Path:  "sub",
+				Name:  "sub",
+				IsDir: true,
+			},
 		}, {
 			name:   "File",
 			remote: "file1",