changes(backend): return 404 if paste not exist

paste/home.py

@@ -5,7 +5,7 @@ from flask import (
     redirect,
     render_template,
     request,
-    url_for,
+    url_for, abort,
 )
 from werkzeug import Response
 
@@ -60,5 +60,9 @@ def get_content(path: str) -> str:
     :return: Paste content.
     """
     db = connect_redis()
-    flash(db.get(path))
+    data = db.get(path)
+    if check_content_exist(path):
+        flash(data)
         return render_template("content.html.j2")
+    else:
+        abort(404)