Fix UiComponent2.consumedProps regression

+ Previously, if `UiComponent2.consumedProps` was an empty list, it would throw a runtime exception.
+ This was a regression in `UiComponent2` for consumers migrating from `UiComponent`.

lib/src/util/map_util.dart

@@ -96,7 +96,7 @@ void forwardUnconsumedProps(Map props, {
   for (String key in props.keys) {
     if (keysToOmit != null && keysToOmit.contains(key)) continue;
 
-    if (keySetsToOmit != null) {
+    if (keySetsToOmit != null && keySetsToOmit.isNotEmpty) {
       /// If the passed in value of [keySetsToOmit] comes from
       /// [addUnconsumedProps], there should only be a single index.
       /// Consequently, this case exists to give the opportunity for the loop

test/over_react/util/map_util_test.dart

@@ -209,6 +209,30 @@ main() {
 
         expect(actual, equals(expected));
       });
+
+      test('when keySetsToOmit is empty', () {
+        var actual = {};
+
+        forwardUnconsumedProps({
+          'prop 1': 'my prop #1',
+          'prop 2': 'my prop #2',
+          'prop 3': 'my prop #3',
+          'prop 4': 'my prop #4',
+          'prop 5': 'my prop #5',
+          'prop 6': 'my prop #6',
+        }, keySetsToOmit: [], propsToUpdate: actual);
+
+        var expected = {
+          'prop 1': 'my prop #1',
+          'prop 2': 'my prop #2',
+          'prop 3': 'my prop #3',
+          'prop 4': 'my prop #4',
+          'prop 5': 'my prop #5',
+          'prop 6': 'my prop #6',
+        };
+
+        expect(actual, equals(expected));
+      });
 
       test('with only valid DOM/SVG props', () {
         var actual = {};