[debugger] tentative fix for crash in FindSharedFunctionInfoInScript.

src/debug/debug.cc

Index: src/debug/debug.cc
diff --git a/src/debug/debug.cc b/src/debug/debug.cc
index 955f86618213482fcee80aa69fc321ddf69ef27a..bd45b71551f94a08c6e1049fd8dc64cfba96731c 100644
--- a/src/debug/debug.cc
+++ b/src/debug/debug.cc
@@ -1300,6 +1300,7 @@ Handle<Object> Debug::FindSharedFunctionInfoInScript(Handle<Script> script,
       closure = finder.ResultClosure();
       shared = finder.Result();
     }
+    if (shared == NULL) break;
     HandleScope scope(isolate_);
     if (closure == NULL) {
       if (!Compiler::CompileDebugCode(handle(shared))) break;