fix: setDatasetAttributes no long overwrites user attributes

* add a test

Author: bogovicj

src/main/java/org/janelia/saalfeldlab/n5/N5Writer.java

@@ -142,7 +142,7 @@ default void setDatasetAttributes(
 			final String datasetPath,
 			final DatasetAttributes datasetAttributes) throws N5Exception {
 
-		setAttribute(datasetPath, "/", getConvertedDatasetAttributes(datasetAttributes));
+		setAttributes(datasetPath, getConvertedDatasetAttributes(datasetAttributes).asMap());
 	}
 
 	/**

src/test/java/org/janelia/saalfeldlab/n5/AbstractN5Test.java

@@ -771,6 +771,21 @@ public void testAttributes() {
 		}
 	}
 
+	@Test
+	public void testDatasetAttributes() {
+
+		final String dset = "";
+		final String key = "user-attr";
+		final String value = "value";
+		try (final N5Writer n5 = createTempN5Writer()) {
+
+			n5.setAttribute(dset, key, value);
+			n5.setDatasetAttributes(dset, new DatasetAttributes(new long[]{5}, new int[]{5}, DataType.INT32));
+			assertNotNull(n5.getDatasetAttributes(dset));
+			assertEquals(value, n5.getAttribute(dset, key, String.class));
+		}
+	}
+
 	@Test
 	public void testNullAttributes() throws URISyntaxException, IOException {