Modifies assertion for possibly null code pointer.

runtime/vm/code_generator.cc

Index: runtime/vm/code_generator.cc
===================================================================
--- runtime/vm/code_generator.cc	(revision 29395)
+++ runtime/vm/code_generator.cc	(working copy)
@@ -1383,6 +1383,7 @@
 DEFINE_RUNTIME_ENTRY(OptimizeInvokedFunction, 1) {
   const Function& function = Function::CheckedHandle(arguments.ArgAt(0));
   ASSERT(!function.IsNull());
+  ASSERT(function.HasCode());
 
   if (CanOptimizeFunction(function, isolate)) {
     const Error& error =
@@ -1441,6 +1442,7 @@
         target_code.EntryPoint());
   }
   arguments.SetReturn(target_code);
+  ASSERT(target_function.HasCode());
 }