[debug] Fix null pointer access in FindSharedFunctionInfo

This fixes a null pointer access in FindSharedFunctionInfo that
was introduced when adding a guard to top level function
compilation.

Bug: chromium:1185540
Change-Id: I24b9752637aba0e660bd8f20be83522e1009b69f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2742194
Commit-Queue: Kim-Anh Tran <kimanh@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73258}

src/debug/debug.cc

@@ -1596,7 +1596,8 @@ Handle<Object> Debug::FindSharedFunctionInfoInScript(Handle<Script> script,
     IsCompiledScope is_compiled_scope;
     {
       shared = FindSharedFunctionInfoCandidate(position, script, isolate_);
-      if (shared.is_null() && iteration == 0) {
+      if (shared.is_null()) {
+        if (iteration > 0) break;
         // It might be that the shared function info is not available as the
         // top level functions are removed due to the GC. Try to recompile
         // the top level functions.

test/inspector/debugger/regression-1185540-expected.txt

+Check that setting a breakpoint in an invalid function is not crashing.
+[]

test/inspector/debugger/regression-1185540.js

+// Copyright 2021 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.
+
+let {session, contextGroup, Protocol} = InspectorTest.start(
+    'Check that setting a breakpoint in an invalid function is not crashing.');
+
+const invalidFunc = `console.l   og('hi');//# sourceURL=invalid.js`;
+
+Protocol.Debugger.enable().then(onDebuggerEnabled);
+
+function onDebuggerEnabled() {
+  Protocol.Runtime.enable();
+  Protocol.Runtime.onExecutionContextCreated(onExecutionContextCreated);
+}
+
+async function onExecutionContextCreated(messageObject) {
+  const executionContextId = messageObject.params.context.id;
+  await testSetBreakpoint(executionContextId, invalidFunc, 'invalid.js');
+}
+
+async function testSetBreakpoint(executionContextId, func, url) {
+  const obj = await Protocol.Runtime.compileScript({
+    expression: func,
+    sourceURL: url,
+    persistScript: true,
+    executionContextId
+  });
+  const scriptId = obj.result.scriptId;
+  const {result: {locations}} =
+      await Protocol.Debugger.setBreakpointByUrl({lineNumber: 0, url});
+  InspectorTest.log(JSON.stringify(locations));
+  InspectorTest.completeTest();
+};