!15514 clean codex

From: @zhupuxu
Reviewed-by: @zhoufeng54,@jjfeing
Signed-off-by: @jjfeing

mindspore/ccsrc/runtime/device/ascend/ascend_kernel_runtime.cc

@@ -955,7 +955,7 @@ int AscendKernelRuntime::DeleteDumpFile(std::string path) {
   if (S_ISREG(statbuf.st_mode)) {
     result = remove(path.c_str());
   } else if (S_ISDIR(statbuf.st_mode)) {
-    if ((dir = opendir(path.c_str())) == NULL) {
+    if ((dir = opendir(path.c_str())) == nullptr) {
       return -1;
     }
 

mindspore/ccsrc/runtime/device/ascend/signal_util.cc

@@ -28,6 +28,7 @@ SignalGuard::~SignalGuard() {
     (void)sigemptyset(&int_action.sa_mask);
     int_action.sa_flags = SA_RESTART | SA_SIGINFO;
     (void)sigaction(SIGINT, &int_action, nullptr);
+    old_handler = nullptr;
   }
 }