Add sanity check.

- The info list can in fact be NULL so we need to guard against that. This
  wouldn't currently get hit though, since the cases where the list isn't
  passed in are those where we only want a minimal frame anyways, so
  variable/return value creation wouldn't even be attempted.

src/apps/debugger/debug_info/DwarfImageDebugInfo.cpp

@@ -673,7 +673,7 @@ DwarfImageDebugInfo::CreateFrame(Image* image,
 			instructionPointer, functionInstance->Address() - fRelocationDelta,
 			subprogramEntry->Variables(), subprogramEntry->Blocks());
 
-		if (!returnValueInfos->IsEmpty()) {
+		if (returnValueInfos != NULL && !returnValueInfos->IsEmpty()) {
 			_CreateReturnValues(returnValueInfos, image, frame,
 				*stackFrameDebugInfo);
 		}