dyndbg: fix old BUG_ON in >control parser

JIRA: https://issues.redhat.com/browse/RHEL-37113
JIRA: https://issues.redhat.com/browse/RHEL-37114
CVE: CVE-2024-35947
MR: !4270

This MR fixes CVE-2024-35947 by preventing a potential BUG_ON() call under certain circumstances.

Signed-off-by: Waiman Long longman@redhat.com