Fix issue 6403: do not crash if super indexed load does not exist (return 'no-such-method call' ins…

runtime/vm/flow_graph_builder.cc

Index: runtime/vm/flow_graph_builder.cc
===================================================================
--- runtime/vm/flow_graph_builder.cc	(revision 14288)
+++ runtime/vm/flow_graph_builder.cc	(working copy)
@@ -2308,10 +2308,12 @@
       // super class instead.
       ArgumentListNode* arguments = new ArgumentListNode(node->token_pos());
       arguments->Add(node->index_expr());
-      BuildStaticNoSuchMethodCall(node->super_class(),
-                                  node->array(),
-                                  index_operator_name,
-                                  arguments);
+      StaticCallInstr* call =
+          BuildStaticNoSuchMethodCall(node->super_class(),
+                                      node->array(),
+                                      index_operator_name,
+                                      arguments);
+      ReturnDefinition(call);
       return;
     }
   }