src: replace FromJust() with Check() when possible

FromJust() is often used not for its return value, but for its
side-effects. In these cases, Check() exists, and is more clear as to
the intent. From its comment:

  To be used, where the actual value of the Maybe is not needed, like
  Object::Set.

See: https://github.com/nodejs/node/pull/26929/files#r269256335

PR-URL: https://github.com/nodejs/node/pull/27162
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>

src/string_decoder.cc

@@ -309,11 +309,11 @@ void InitializeStringDecoder(Local<Object> target,
 
   target->Set(context,
               FIXED_ONE_BYTE_STRING(isolate, "encodings"),
-              encodings).FromJust();
+              encodings).Check();
 
   target->Set(context,
               FIXED_ONE_BYTE_STRING(isolate, "kSize"),
-              Integer::New(isolate, sizeof(StringDecoder))).FromJust();
+              Integer::New(isolate, sizeof(StringDecoder))).Check();
 
   env->SetMethod(target, "decode", DecodeData);
   env->SetMethod(target, "flush", FlushData);