Make MojoWaitMany() accept zero handles.

mojo/public/c/system/tests/wait_unittest.cc

Index: mojo/public/c/system/tests/wait_unittest.cc
diff --git a/mojo/public/c/system/tests/wait_unittest.cc b/mojo/public/c/system/tests/wait_unittest.cc
index 541043e08106ad5db78121be3f038b9e16180fd0..9eba943bd9185592a06560970f983b0d014b70c3 100644
--- a/mojo/public/c/system/tests/wait_unittest.cc
+++ b/mojo/public/c/system/tests/wait_unittest.cc
@@ -25,6 +25,21 @@ TEST(WaitTest, InvalidHandle) {
       MojoWaitMany(&h, &sig, 1u, MOJO_DEADLINE_INDEFINITE, nullptr, nullptr));
 }
 
+TEST(WaitTest, WaitManyNoHandles) {
+  EXPECT_EQ(MOJO_RESULT_DEADLINE_EXCEEDED,
+            MojoWaitMany(nullptr, nullptr, 0u, static_cast<MojoDeadline>(0),
+                         nullptr, nullptr));
+
+  // The |result_index| argument is optional, so make sure it doesn't touch it
+  // even if it's non-null.
+  // TODO(vtl): The same is true for the |signals_states| argument.
+  uint32_t result_index = static_cast<uint32_t>(-1);
+  EXPECT_EQ(MOJO_RESULT_DEADLINE_EXCEEDED,
+            MojoWaitMany(nullptr, nullptr, 0u, static_cast<MojoDeadline>(1000),
+                         &result_index, nullptr));
+  EXPECT_EQ(static_cast<uint32_t>(-1), result_index);
+}
+
 // TODO(vtl): Write tests that actually test waiting.
 
 }  // namespace