minor #2855 Encourage using prepared statements (ntzm)

This PR was submitted for the 2.x branch but it was merged into the 1.x branch instead (closes #2855).

Discussion
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Encourage using prepared statements

Although the previous code isn't vulnerable, it could be if copied and used to store user input.

Commits
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97d9dc04 Encourage using prepared statements

doc/recipes.rst

@@ -409,8 +409,8 @@ First, let's create a temporary in-memory SQLite3 database to work with::
     {% block content %}Hello {{ name }}{% endblock %}
     ';
     $now = time();
-    $dbh->exec("INSERT INTO templates (name, source, last_modified) VALUES ('base.twig', '$base', $now)");
-    $dbh->exec("INSERT INTO templates (name, source, last_modified) VALUES ('index.twig', '$index', $now)");
+    $dbh->prepare('INSERT INTO templates (name, source, last_modified) VALUES (?, ?, ?)')->execute(['base.twig', $base, $now]);
+    $dbh->prepare('INSERT INTO templates (name, source, last_modified) VALUES (?, ?, ?)')->execute(['index.twig', $index, $now]);
 
 We have created a simple ``templates`` table that hosts two templates:
 ``base.twig`` and ``index.twig``.