Weaken an assert in the message handler

runtime/vm/os_thread_win.cc

Index: runtime/vm/os_thread_win.cc
diff --git a/runtime/vm/os_thread_win.cc b/runtime/vm/os_thread_win.cc
index 7af1ce41d96914a5ef52aff1cecf60ca71efc552..8fd13c94dfb79b1b3f446f66327ebb4ed0aeedc0 100644
--- a/runtime/vm/os_thread_win.cc
+++ b/runtime/vm/os_thread_win.cc
@@ -118,7 +118,6 @@ void OSThread::Join(ThreadJoinId id) {
   // Second OSThread could be refactored to no longer be AllStatic. Then the
   // handle could be cached in the object by the Start method.
   if (handle == NULL) {
-    ASSERT(GetLastError() == ERROR_INVALID_PARAMETER);
     return;
   }