docs: add empty lines

I don't know why, but without these empty lines, PhpStorm's Structure
window does not show correct structure.

Author: kenjis

user_guide_src/source/database/queries.rst

@@ -80,6 +80,7 @@ You can get the current prefix any time with this method:
 
 .. literalinclude:: queries/006.php
 
+
 **********************
 Protecting Identifiers
 **********************
@@ -105,6 +106,7 @@ prefixing set ``true`` (boolean) via the second parameter:
 
 .. literalinclude:: queries/008.php
 
+
 ***************
 Escaping Values
 ***************
@@ -196,6 +198,7 @@ example:
 
 .. literalinclude:: queries/015.php
 
+
 ****************
 Prepared Queries
 ****************