Fix issue 5517 by setting the successors the right way in a try/catch.

lib/compiler/implementation/ssa/validate.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class HValidator extends HInstructionVisitor {
   bool isValid = true;
   HGraph graph;
 
   void visitGraph(HGraph visitee) {
     graph = visitee;
@@ skipping 19 matching lines @@
     if (block.last is !HControlFlow) {
       markInvalid("block ends with non-tail node.");
     }
     if (block.last is HIf && block.successors.length != 2) {
       markInvalid("If node without two successors");
     }
     if (block.last is HConditionalBranch && block.successors.length != 2) {
       markInvalid("Conditional node without two successors");
     }
     if (block.last is HGoto && block.successors.length != 1) {
-      markInvalid("Goto node without one successor");
+      markInvalid("Goto node with not exactly one successor");
     }
     if (block.last is HJump && block.successors.length != 1) {
       markInvalid("Break or continue node without one successor");
     }
     if (block.last is HReturn &&
         (block.successors.length != 1 || !block.successors[0].isExitBlock())) {
       markInvalid("Return node with > 1 succesor or not going to exit-block");
     }
     if (block.last is HExit && !block.successors.isEmpty()) {
       markInvalid("Exit block with successor");
@@ skipping 119 matching lines @@
       markInvalid("Instruction in wrong block");
     }
     if (!hasCorrectInputs()) {
       markInvalid("Incorrect inputs");
     }
     if (!hasCorrectUses()) {
       markInvalid("Incorrect uses");
     }
   }
 }