fix: remove parentIsObject() check (#12851)

we will allow situations such as

```
a/b/1.txt
a/b
```

and

```
a/b
a/b/1.txt
```

we are going to document that this usecase is
not supported and we will never support it, if
any application does this users have to delete
the top level parent to make sure namespace is
accessible at lower level.

rest of the situations where the prefixes get
created across sets are supported as is.

cmd/xl-storage_test.go

@@ -1628,8 +1628,8 @@ func TestXLStorageRenameFile(t *testing.T) {
 	}
 }
 
-// TestXLStorage xlStorage.CheckFile()
-func TestXLStorageCheckFile(t *testing.T) {
+// TestXLStorage xlStorage.StatInfoFile()
+func TestXLStorageStatInfoFile(t *testing.T) {
 	// create xlStorage test setup
 	xlStorage, path, err := newXLStorageTestSetup()
 	if err != nil {
@@ -1699,19 +1699,20 @@ func TestXLStorageCheckFile(t *testing.T) {
 		{
 			srcVol:      "non-existent-vol",
 			srcPath:     "success-file",
-			expectedErr: errPathNotFound,
+			expectedErr: errVolumeNotFound,
 		},
 		// TestXLStorage case - 7.
 		// TestXLStorage case with file with directory.
 		{
 			srcVol:      "success-vol",
 			srcPath:     "path/to",
-			expectedErr: errFileNotFound,
+			expectedErr: nil,
 		},
 	}
 
 	for i, testCase := range testCases {
-		if err := xlStorage.CheckFile(context.Background(), testCase.srcVol, testCase.srcPath); err != testCase.expectedErr {
+		_, err := xlStorage.StatInfoFile(context.Background(), testCase.srcVol, testCase.srcPath+"/"+xlStorageFormatFile)
+		if err != testCase.expectedErr {
 			t.Errorf("TestXLStorage case %d: Expected: \"%s\", got: \"%s\"", i+1, testCase.expectedErr, err)
 		}
 	}