Fix default memcache size to 100MB (#2960)

* Fix default memcache size to 100MB

* Deal with empty annotation of 'No Object' label images

---------
Signed-off-by: Songki Choi <songki.choi@intel.com>

src/otx/algorithms/classification/configs/configuration.yaml

@@ -441,7 +441,7 @@ algo_backend:
     warning: null
   mem_cache_size:
     affects_outcome_of: TRAINING
-    default_value: 1000000000
+    default_value: 100000000
     description: Size of memory pool for caching decoded data to load data faster (bytes).
     editable: true
     header: Size of memory pool

src/otx/algorithms/common/adapters/mmcv/pipelines/load_image_from_otx_dataset.py

@@ -204,6 +204,8 @@ def __call__(self, results: Dict[str, Any]) -> Dict[str, Any]:
             return cached_results
         results = self._load_img(results)
         results = self._load_ann_if_any(results)
+        if results is None:
+            return None
         results.pop("dataset_item", None)  # Prevent deepcopy or caching
         results = self._resize_img_ann_if_any(results)
         self._save_cache(results)