fix an error when executing startup.bat when the log directory exists (#5213)

Co-authored-by: 吴晟 Wu Sheng <wu.sheng@foxmail.com>

dist-material/bin/webappService.bat

@@ -22,7 +22,7 @@ set WEBAPP_HOME=%~dp0%..
 set JARPATH=%WEBAPP_HOME%\webapp
 set WEBAPP_LOG_DIR=%WEBAPP_HOME%\logs
 
-if exist "%WEBAPP_LOG_DIR%" (
+if not exist "%WEBAPP_LOG_DIR%" (
     mkdir "%WEBAPP_LOG_DIR%"
 )