[JENKINS-21631] - Don't fail with NPE if the PeepholePermalink cache contains the non-numeric value.

Actually, the change just prevents symptoms. There should be an error somewhere else.

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>
Merge branch 'JENKINS-21631' of github.com:synopsys-arc-oss/jenkins
[FIXED JENKINS-21631] Noting #1275.