Fix occasional assert failure when disassembling: move assert to proper place.

runtime/vm/object.cc

Index: runtime/vm/object.cc
===================================================================
--- runtime/vm/object.cc	(revision 45647)
+++ runtime/vm/object.cc	(working copy)
@@ -12047,9 +12047,9 @@
 
 
 RawLocalVarDescriptors* Code::GetLocalVarDescriptors() const {
-  ASSERT(!is_optimized());
   const LocalVarDescriptors& v = LocalVarDescriptors::Handle(var_descriptors());
   if (v.IsNull()) {
+    ASSERT(!is_optimized());
     const Function& f = Function::Handle(function());
     ASSERT(!f.IsIrregexpFunction());  // Not yet implemented.
     Compiler::ComputeLocalVarDescriptors(*this);