Avoid reinitialize package-initialize

Solve warning of emacs 27+ when in personal scripts it previously
already initialize it.

Author: ryukinix

core/prelude-packages.el

@@ -51,7 +51,9 @@
 
 ;; set package-user-dir to be relative to Prelude install path
 (setq package-user-dir (expand-file-name "elpa" prelude-dir))
-(package-initialize)
+
+(unless package--initialized
+    (package-initialize))
 
 ;; install & enable use-package
 (unless (package-installed-p 'use-package)