Avoid crashing when Runtime_GetFrameDetails is called on a RunMicrotasks stack frame

src/runtime.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 <stdlib.h>
 #include <limits>
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
@@ skipping 11384 matching lines @@
   details->set(kFrameDetailsConstructCallIndex, heap->ToBoolean(constructor));
 
   // Add the at return information.
   details->set(kFrameDetailsAtReturnIndex, heap->ToBoolean(at_return));
 
   // Add flags to indicate information on whether this frame is
   //   bit 0: invoked in the debugger context.
   //   bit 1: optimized frame.
   //   bit 2: inlined in optimized frame
   int flags = 0;
-  if (*save->context() == *isolate->debug()->debug_context()) {
+  if (!save->context().is_null() &&
+      *save->context() == *isolate->debug()->debug_context()) {
     flags |= 1 << 0;
   }
   if (is_optimized) {
     flags |= 1 << 1;
     flags |= inlined_jsframe_index << 2;
   }
   details->set(kFrameDetailsFlagsIndex, Smi::FromInt(flags));
 
   // Fill the dynamic part.
   int details_index = kFrameDetailsFirstDynamicIndex;
@@ skipping 3797 matching lines @@
   }
   return NULL;
 }
 
 
 const Runtime::Function* Runtime::FunctionForId(Runtime::FunctionId id) {
   return &(kIntrinsicFunctions[static_cast<int>(id)]);
 }
 
 } }  // namespace v8::internal