Add missing initialization in tokenize_expand_file() for output list

This should have been added in efc9816, but it looks like I have found a
way to mess up a bit a patch split.  This should have no consequence in
practice, but let's be clean.

Discussion: https://postgr.es/m/Y324HvGKiWxW2yxe@paquier.xyz

src/backend/libpq/hba.c

@@ -489,7 +489,7 @@ tokenize_expand_file(List *tokens,
 {
 	char	   *inc_fullname;
 	FILE	   *inc_file;
-	List	   *inc_lines;
+	List	   *inc_lines = NIL;
 	ListCell   *inc_line;
 
 	inc_fullname = AbsoluteConfigLocation(inc_filename, outer_filename);