OSU server: Print out signup ID if there is some problem with it

Signed-off-by: Ben Greear <greearb@candelatech.com>

hs20/server/www/signup.php

@@ -17,7 +17,7 @@ if (!$db) {
 
 $row = $db->query("SELECT realm FROM sessions WHERE id='$id'")->fetch();
 if ($row == false) {
-   die("Session not found");
+   die("Session not found for id: $id");
 }
 $realm = $row['realm'];