Apply suggestions from code review

Co-authored-by: Daeyeon Jeong <daeyeon.dev@gmail.com>

Author: jasnell

src/node_file.cc

@@ -1409,7 +1409,7 @@ static void ReadLink(const FunctionCallbackInfo<Value>& args) {
     Local<Value> ret;
     if (!StringBytes::Encode(isolate, link_path, encoding, &error)
              .ToLocal(&ret)) {
-      DCHECK(!ret.IsEmpty());
+      DCHECK(!error.IsEmpty());
       env->isolate()->ThrowException(error);
       return;
     }
@@ -1968,7 +1968,7 @@ static void RealPath(const FunctionCallbackInfo<Value>& args) {
     Local<Value> ret;
     if (!StringBytes::Encode(isolate, link_path, encoding, &error)
              .ToLocal(&ret)) {
-      DCHECK(!ret.IsEmpty());
+      DCHECK(!error.IsEmpty());
       env->isolate()->ThrowException(error);
       return;
     }
@@ -2063,7 +2063,7 @@ static void ReadDir(const FunctionCallbackInfo<Value>& args) {
       Local<Value> fn;
       if (!StringBytes::Encode(isolate, ent.name, encoding, &error)
                .ToLocal(&fn)) {
-        DCHECK(!fn.IsEmpty());
+        DCHECK(!error.IsEmpty());
         isolate->ThrowException(error);
         return;
       }