[Bugfix] Fix Qwen-Image min-size normalization for tiny requests (#2637)

Signed-off-by: David Chen <530634352@qq.com>

tests/diffusion/models/qwen_image/test_qwen_image_size_utils.py

@@ -0,0 +1,26 @@
+import pytest
+
+from vllm_omni.diffusion.utils.size_utils import (
+    normalize_min_aligned_size,
+)
+
+pytestmark = [pytest.mark.core_model, pytest.mark.cpu]
+
+
+@pytest.mark.parametrize(
+    ("height", "width", "expected"),
+    [
+        (1, 1, (16, 16)),
+        (15, 15, (16, 16)),
+        (17, 17, (16, 16)),
+        (31, 33, (16, 32)),
+        (64, 80, (64, 80)),
+    ],
+)
+def test_normalize_min_aligned_size_clamps_to_minimum_aligned_shape(height, width, expected):
+    assert normalize_min_aligned_size(height, width, alignment=16) == expected
+
+
+def test_normalize_min_aligned_size_rejects_invalid_alignment():
+    with pytest.raises(ValueError, match="positive alignment"):
+        normalize_min_aligned_size(16, 16, alignment=0)