fs: fix file descriptor validator

Author: anonrig

lib/fs.js

@@ -131,7 +131,7 @@ const {
   CHAR_BACKWARD_SLASH,
 } = require('internal/constants');
 const {
-  isUint32,
+  isInt32,
   parseFileMode,
   validateBoolean,
   validateBuffer,
@@ -201,7 +201,7 @@ function makeStatsCallback(cb) {
   };
 }
 
-const isFd = isUint32;
+const isFd = isInt32;
 
 function isFileType(stats, fileType) {
   // Use stats array directly to avoid creating an fs.Stats instance just for