Fix num_trials calculation on dataset length less than num_class (#4014)

Fix balanced sampler

src/otx/algo/samplers/balanced_sampler.py

@@ -65,7 +65,7 @@ def __init__(
         self.img_indices = {k: torch.tensor(v, dtype=torch.int64) for k, v in ann_stats.items() if len(v) > 0}
         self.num_cls = len(self.img_indices.keys())
         self.data_length = len(self.dataset)
-        self.num_trials = int(self.data_length / self.num_cls)
+        self.num_trials = max(int(self.data_length / self.num_cls), 1)
 
         if efficient_mode:
             # Reduce the # of sampling (sampling data for a single epoch)