build: do not cd on vcbuild help

`vcbuild help` just outputs help info and exits.

If a user calls this command not from a project root,
the directory change can be unexpected and unwanted.

PR-URL: https://github.com/nodejs/node/pull/19291
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

vcbuild.bat

@@ -1,7 +1,5 @@
 @if not defined DEBUG_HELPER @ECHO OFF
 
-cd %~dp0
-
 if /i "%1"=="help" goto help
 if /i "%1"=="--help" goto help
 if /i "%1"=="-help" goto help
@@ -11,6 +9,8 @@ if /i "%1"=="-?" goto help
 if /i "%1"=="--?" goto help
 if /i "%1"=="/?" goto help
 
+cd %~dp0
+
 @rem Process arguments.
 set config=Release
 set target=Build