Fixed assert causing crash when attempting to load a library from an invalid path.

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index 428dfa34b299bd70cb87a437ba5eca91c0c33fa3..ac586d969d51a2109635fb419c67c781803cafd7 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -11008,8 +11008,8 @@ bool LibraryPrefix::LoadLibrary() const {
       Exceptions::PropagateError(Error::Cast(obj));
     }
   } else {
-    // Another load request is in flight.
-    ASSERT(deferred_lib.LoadRequested());
+    // Another load request is in flight or previously failed.
+    ASSERT(deferred_lib.LoadRequested() || deferred_lib.LoadFailed());
   }
   return false;  // Load request not yet completed.
 }