add test to cover partial branch in load_kasvs_ecdh_vectors

The loop to find supported parameter sets is partially covered otherwise
diff --git a/tests/test_utils.py b/tests/test_utils.py
index 416de79..210e929 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -3045,6 +3045,10 @@
     assert expected == load_kasvs_dh_vectors(vector_data)
 
 
+def test_load_kasvs_ecdh_vectors_empty_vector_data():
+    assert [] == load_kasvs_ecdh_vectors([])
+
+
 def test_load_kasvs_ecdh_vectors():
     vector_data = textwrap.dedent("""
     #  CAVS 11.0