[BUG] Open Images dataset ignores classes requirement
### System information

-   **OS Platform and Distribution (e.g., Linux Ubuntu 16.04)**: macOS
-   **FiftyOne installed from (pip or source)**: source
-   **FiftyOne version (run `fiftyone --version`)**: 0.11.2.1
-   **Python version**: 3.6.8

### Describe the problem

In the example below, `dataset` should only contain samples with houses, but it contains all downloaded samples:

```py
import fiftyone as fo
import fiftyone.zoo as foz
from fiftyone import ViewField as F

# Download some samples
foz.load_zoo_dataset(
    "open-images-v6",
    split="validation",
    max_samples=50,
)

# This should only contain samples with houses, but actually contains all downloaded samples
dataset = foz.load_zoo_dataset(
    "open-images-v6",
    split="validation",
    classes=["House"],
)

# Verify that some non-House samples exist
no_houses = dataset.match(F("detections.detections").filter(F("label") == "House").length() == 0)
print(len(no_houses))  # should be zero, but isn't
```
diff --git a/fiftyone/utils/openimages.py b/fiftyone/utils/openimages.py
index f06261e52..1f632a324 100644
--- a/fiftyone/utils/openimages.py
+++ b/fiftyone/utils/openimages.py
@@ -311,7 +311,12 @@ class OpenImagesV6DatasetImporter(foud.LabeledImageDatasetImporter):
             valid_ids = all_label_ids + not_all_ids + extra_ids
             valid_ids = valid_ids[:max_samples]
         else:
-            valid_ids = sorted(image_ids)
+            if self.classes is None and self.attrs is None:
+                # No requirements were provided, so always make all samples
+                # available
+                valid_ids = sorted(image_ids)
+            else:
+                valid_ids = sorted(any_label_ids)
 
             if shuffle:
                 random.shuffle(valid_ids)
['fiftyone/utils/openimages.py']