[debugger] tentative fix for crash in FindSharedFunctionInfoInScript.

src/debug/debug.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/debug/debug.h"
 
 #include "src/api.h"
 #include "src/arguments.h"
 #include "src/bootstrapper.h"
 #include "src/code-stubs.h"
@@ skipping 1282 matching lines @@
         } else {
           continue;
         }
         if (candidate->script() == *script) {
           finder.NewCandidate(candidate, candidate_closure);
         }
       }
       closure = finder.ResultClosure();
       shared = finder.Result();
     }
+    if (shared == NULL) break;
     HandleScope scope(isolate_);
     if (closure == NULL) {
       if (!Compiler::CompileDebugCode(handle(shared))) break;
     } else {
       if (!Compiler::CompileDebugCode(handle(closure))) break;
     }
   }
   return isolate_->factory()->undefined_value();
 }
 
@@ skipping 1091 matching lines @@
 }
 
 
 void LockingCommandMessageQueue::Clear() {
   base::LockGuard<base::Mutex> lock_guard(&mutex_);
   queue_.Clear();
 }
 
 }  // namespace internal
 }  // namespace v8